README_ULUG.TXT - Readme file for Urban Land-Use Gradient 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). In rare instances, a compound is reported at estimated concentrations above the standard LRL because of laboratory uncertainty about the actual concentration measured. These problems are usually related to the performance of the laboratory instruments, interference created by other compounds in the water sample (such as hydrogen sulfide), or inherent instability of the compound being measured. QUALITY ASSURANCE/QUALITY CONTROL SAMPLES The water-quality data tables provided on this website are only for environmental samples (actual surface water samples). In addition to the environmental samples, the NECB study collected quality assurance/quality control (qa/qc) samples. For every 15-20 environmental surface-water samples collected, the following set of quality-control samples were collected: 1. Field blanks for nutrients and pesticides. 2. Field spikes and field spike replicates for pesticides. 3. One (1) lab spike for pesticides. 4. Field replicates for nutrients and pesticides. See Socolow and others (2000), page 22, for an explanation of types of qa/qc samples. The qa/qc sample results are not available on the website, however the following is a brief summary of the qa/qc sample results: -All pesticide blank concentrations were below detection or at estimated concentrations below the LRL. Recoveries on the pesticide field spikes generally were near 100 percent. -Concentrations of certain nutrients were detected in some of the blank samples. However, these concentrations were usually at estimated concentrations below the LRL and much lower than the concentrations in the environmental samples. -All relative differences measured in concentrations between replicate and environmental samples were within the precision of the method for the specific analyte at a particular concentration range. Anyone wishing to obtain the qa/qc data, please contact Kim Campo of the NECB study unit at kcampo@usgs.gov. 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 Socolow, R.S., Zanca, J.L., Murino, Jr., Domenic, and Ramsbey, L.R., 2000, Water resources data, Massachusetts and Rhode Island, Water Year 1999: U.S. Geological Survey Water-Data Report MA-RI-99-1, 401 p.