Because the WRIA 1 study area lies in both the United States and Canada, two well-numbering systems are used in these webpages. Both well-numbering systems are based on the geographic locations of the wells. Wells located within the United States are identified by the well-numbering system used in the State of Washington, and wells located within Canada are identified by the well-numbering system used by the British Columbia Ministry of Environment (BC Environment).

The well-numbering system used in the State of Washington is based on the rectangular grid system of the Public Land Survey (see figure a). The Willamette baseline and meridian form the basis of a grid system that indicates township, range, section, and 40-acre tract. The well number is created by first listing the number of the township and range, followed by the section number and the letter representing the 40-acre subsection. For example, well 39N/03E-12R02 is located in township 39 north and range 3 east, which is north and east of the Willamette baseline and meridian. Following the hyphen, the two-digit number indicates that the well is in section 12. The letter ("R") indicates the appropriate 40-acre tract within the section, as shown on figure a. The last number (02) is the sequence number and indicates that this is the second well in this tract added to the USGS database. In instances where a spring has been inventoried as a ground-water site, the local number ends with an "S".

The well-numbering system used by BC Environment is based on divisions of the primary quadrangles of the National Topographic System of Canada. Each primary quadrangle is 4 degrees of latitude by 8 degrees of longitude. For purposes of numbering wells, the quadrangles are subdivided as shown in figure b. Each primary quadrangle is first subdivided into 16 areas of 1 degree of latitude by 2 degrees of longitude, each of which is identified by a letter. These areas then are subdivided into 100 6-minute by 12-minute numbered areas that are identified by 3-digit numbers and are further subdivided through a process of 3 successive quarterings. Each successive quartering is numbered as shown in figure b, producing a three-digit number of the form "1.2.3." The final sub-divisions are 45 seconds of latitude by 1 minute and 30 seconds of longitude and cover about 590 acres each. Wells located within this final subdivision are numbered sequentially from one, and the sequential number is added to the subdivision identifier. For example, well 92G.008.1.2.3-12 indicates that this well is the twelfth well inventoried by BC Environment in the 45 second by 1 minute 30 second subdivision identified as 92G.008.1.2.3. In wells where nested piezometers have been installed, the individual piezometer cannot be distinguished by the well local number. In those cases the depth of the bottom of the screened-interval has been added to the end of the local number as in well 092G.009.1.1.1-12(25). Wells that do not have BC Environment assigned sequence numbers have been designated as XX or in cases where the well in question is a monitoring well installed by Environment Canada (EC), the EC monitoring well number has been used, as in 092G.008.1.1.4-ABB1.