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The chlorophyll a criteria attainment assessment procedural steps are as follows: 
1. A database was compiled for the three-year assessment period containing the 
following: 
- Long-term CBP stations (records stored in CIMS database); 
- DATAFLOW verification stations (records stored in CIMS database); 
- DATAFLOW cruise-tracks (records stored by VIMS, HRSD, MD DNR); and 
- VA DEQ stations where applicable (records stored in VA DEQ CEDS database). 
2. Only data meeting appropriate QA/QC requirements are used in the assessment. 
Cruise-track data flagged with codes related to equipment failure or sampling 
artifacts were excluded, while data taken during algal blooms were used. 
3. Each segment (e.g., JMSTFL, JMSTFU, JMSOH, JMSMH, and JMSPH - 
refer to Chapter II, Table II-1 in this document for segment nomenclature and 
water body names) is interpolated separately using only the stations and cruise- 
tracks contained in them and directly adjacent. Data from a given day is 
interpolated for a segment if: 1) there were two or more fixed stations sampled 
on that day in that segment; 2) that segment was targeted by a DATAFLOW 
cruise-track on that day; or 3) there was a fixed station sampled in that segment 
and an adjacent segment was targeted by a DATAFLOW cruise-track on that 
day. The last condition takes advantage of cruise-tracks that cross over into 
multiple Chesapeake Bay Program segments. 
4. Datasets are imported into the Chesapeake Bay Interpolator and transformed 
(natural log) prior to interpolation, as chlorophyll a measurements tend to 
follow a log-normal distribution. The program defaults for search area (25 km 2 ) 
and maximum sample size (4) are used, and the “2D Inverse-Distance 
Squared’’ algorithm is chosen. The Interpolator automatically back-transforms 
interpolated estimates before creating the output files. 
5. Interpolator output was organized by segment-season-year. For each interpo¬ 
lator cell in a segment, a season-year (e.g., Spring 2005) average is calculated. 
6. For the VA example, grid-cell averages were then assessed against segment- 
season criteria specified by the VA DEQ Water Quality Assessment Guidance 
Manual for Y2008 303(d)/305(b) Integrative Water Quality Report {VA DEQ 
2007). Values over the criteria were assessed as non-attaining; those equal to or 
less than were assessed as attaining. 
7. Seasonal CFDs are generated for each segment using the steps outlined in 
Chapter 2 of Ambient Water Quality Criteria for Dissolved Oxygen , Water 
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries - 
2007 Addendum (U.S. EPA 2007a). Assessment curves were compared 
against a default reference curve (U.S. EPA 2003). Non-attainment is calcu¬ 
lated by subtracting the area of the reference curve from the area under the 
chlorophyll a criteria assessment curve. 
TYPES OF OUTPUT 
Three types of output were produced for assessment: cumulative frequency 
distribution diagrams, maps, and tabular summaries (see Figure V-l, Figure V-2, and 
Table V-l for examples). 
chapter v 
Chlorophyll a Criteria Assessment Procedures 
