Water System Design Manual
Appendix B: Copies of Selected Guidelines Referenced
Well Field Designation Guideline
Definition of "well field" with notes on monitoring requirements for well fields
Provide a definition of well field to help DOH staff determine utility compliance
with inorganic and organic water quality monitoring
The Department of Health (DOH) recognizes the concept of considering nearby wells drawing
from the same aquifer as a well field, and eligible for consideration as a single source when
determining compliance with water quality monitoring requirements. This guidance to staff
should ensure consistency when dealing with well field designations for Washington State water
DOH may consider two or more individual wells a well field if all of the following criteria are
The depth of all individual wells must be within 20 percent of each other after taking
wellhead elevation differences into account. The depth of the well shall be the distance
from the top of the well to the well screen(s), perforations, or the water bearing strata.
All individual wells shall draw from the same aquifer(s) as determined by comparable
inorganic chemical analysis (such as conductivity, total hardness, nitrates, chlorides or
other information acceptable to DOH), or an evaluation of the well logs or water well
reports for all of the wells being considered..
All individual wells must discharge water through a common pipe with a sampling port
where a sample that includes water from all the individual wells within the well field can
be collected. There shall be no individual service connections prior to the well field
All individual wells must be under the control of the same purveyor to be considered part
of a well field.
The following monitoring requirements apply to all designated well fields:
All individual wells, which are normally in operation during the sampling month, must be
pumping when collecting a source sample.
Samples from a designated well field cannot be composited with samples from any other
drinking water sources.
The water system purveyor shall provide the necessary information to justify varying from this
guideline. DOH regional staff must concur with all variances from this guideline.