README_MERC.TXT - Readme file for Mercury Study - NAWQA NECB

FILE FORMATS

The data tables are offered in two formats, Microsoft Excel and ASCII plain text.
The text files are tables provided in tab-delimited columns with the first row 
being the Column Header Names. The data are preceded by lines of documentation 
or explanatory text. Any row containing such comments starts with a '#' sign. 

These ASCII files are easily viewable in a web browser or any word-processing 
program like MS Word or Notepad. However, those programs will not format the data
into correctly-aligned columns, because the files are tab-delimited (the columns 
do not have fixed widths). These tables are provided with the intention that they
will be easily imported into a spreadsheet or database program (such as Quattro 
Pro, SAS, Access, Paradox, etc.).


WHAT IS A DETECTION?

Until recently (2000), results of laboratory analyses by the USGS were reported
either as quantified above or below (using the less than, <, symbol) a 
Laboratory Reporting Level (LRL). Recent improvements in laboratory analytical
techniques, however, enable a chemist to report an estimated concentration (E) 
when a compound meets all identification criteria, but the concentration value 
is less than the LRL (Connor and others, 1998; Childress and others, 1999).


QUALITY ASSURANCE/QUALITY CONTROL SAMPLES

The water-quality data tables provided on this website include all control 
(qa/qc) samples taken in this study. For water and sediment samples multiple 
samples were taken at 7 sites over the 3 year period.  Results indicate little 
change in Hg concentrations in sediment or stream water over the study period 
at all except one site. Stony Brook had a 10-fold increase in total Hg sediment
concentrations between 1999 and 2000, suggesting a possible point source 
contamination between collection times. For fish tissue samples duplicate samples
were taken at 6 sites, and a triplicate sample at one site. Multiple sunfish 
species were collected at 5 sites. The duplicate and triplicate fish tissue 
samples indicated there were not inconsistencies in sample collection or analysis. 

The Mousam River site near Sanford, ME was located directly below a potential 
point source (landfill). Data from this site were excluded from any data analysis.


REFERENCES

Childress, C.J.O., Foreman, W.T., Connor, B.F., and Maloney, T.J., 1999, New
reporting procedures based on long-term method detection levels and some 
considerations for interpretations of water-quality data provided by the U.S.
Geological Survey National Water Quality Laboratory: U.S. Geological Survey 
Open-File Report 99-193, available ON-LINE at 
http://water.usgs.gov/owq/OFR_99-193/index.html

Connor, B.F., Rose, D.L., Noriega, M.C., Murtagh, L.K., and Abney, S.R., 
1998, Methods of analysis by the U.S. Geological Survey National Water 
Quality Laboratory--Determination of 86 volatile organic compounds in water
by gas chromatography/mass spectrometry, including detections less than 
reporting limits: U.S. Geological Survey Open-File Report 97-829, 78 p.,
available ON-LINE at http://nwql.usgs.gov/Public/pubs/OFR97-829.html