63 
assessing attainment of 30-day mean and instantaneous minimum dissolved oxygen 
criteria within these five segments are cautioned to not automatically assume attain¬ 
ment of the 30-day mean criterion reflects attainment of the instantaneous minimum 
criterion (Table V-9). Site-specific buoy deployments may be necessary to either 
better quantify a relationship or assess attainment using both low- and high- 
frequency data sources. 
Seven segments with only open-water designated uses had a large number of data 
points in quadrant 1 (both criteria were achieved) and in quadrant 4 (instantaneous 
minimum criterion achieved, but the 30-day mean criterion not achieved) and none 
or very few data points in other quadrants were marked in bold typeface in Table V- 
8. These seven segments were: upper (MPNTF) and lower (MPNOH) Mattaponi, 
upper (PMKTF) and lower (PMKOH) Pamunkey River, Eastern Branch Elizabeth 
River (EBEMH), Wicomico River (WICMH), and upper Pocomoke River (POCTF.) 
The segments in the Pamunkey and Mattaponi rivers (segments PMKTF, PMKOH 
and MPNTF, MPNOH, respectively) are known to be strongly influenced by rela¬ 
tively large expanses of fringing wetlands along the entire length of both tidal rivers. 
The Wicomico River (WICMH) and upper Pocomoke River (POCTF) also have 
large areas of tidal wetlands along particular reaches of these two rivers. The natural 
influences of extensive fringing tidal wetlands systems, described in more detail in 
Chapter 6, are the likely reason for why the 30-day mean/instantaneous minimum 
relationship does not fully apply to these seven segments. More site specific evalua¬ 
tion of the data and conditions within the Eastern Branch of the Elizabeth River 
(EBEMH) is required to understand what’s happening in this tidal system. 
Users assessing attainment of the 30-day mean and instantaneous minimum 
dissolved oxygen criteria within these seven segments are cautioned not to automat¬ 
ically assume that attainment of the 30-day mean criterion reflects attainment of the 
instantaneous minimum criterion (Table V-9). Site-specific buoy deployments may 
be necessary either to better quantify a relationship or assess attainment using both 
low- and high-frequency data sources. 
For the remaining seven segments with only open-water designated uses, there were 
insufficient buoy data available to assess whether attainment of the 30-day mean 
criterion reflected attainment of the instantaneous minimum criterion. These 
segments are marked with a “N/D” in Table V-9. 
Of the thirteen segments with deep-water or deep-water and deep-channel desig¬ 
nated uses, eleven of the segments had the vast majority (greater than two-thirds) of 
their open-water designated use data points in quadrant 1 (Table V-8), directly 
supporting the assessment of attainment of the instantaneous minimum criterion 
directly based on assessment of attainment of the 30-day mean criterion in these 
segments (Table V-9). Users assessing attainment of the 30-day mean and instanta¬ 
neous minimum dissolved oxygen criteria within the lower Patuxent River 
(PAXMH) and Southern Branch Elizabeth River (SBEMH) are cautioned not to 
automatically assume that attainment of the 30-day mean criterion reflects attain¬ 
ment of the instantaneous minimum criterion. 
chapter v 
Guidance for Attainment Assessment of instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 
