Water System Design Manual
7.8.2 Drilling Fluids and Well Contamination
It is possible to introduce bacterial or organic contaminants (tetrahydrofuran, toluene, 2-
butanone) during well construction. Therefore, purveyors should properly disinfect and purge
new sources before collecting samples for water quality testing.
7.8.3 Criteria for Multiple Sources or Multiple Pumps per Source
DOH encourages water systems to have multiple supply sources. These sources may offset
recommended standby storage (SB) volumes.
DOH recognizes that multiple pumps for a single source may be more reliable than a single-
pump source. However, we do not consider a single source with multiple-pumps to be as reliable
as multiple sources. The following criteria apply to "multiple pumps in a single source" when
evaluating any reduction in SB volumes (see Section 9.0.4(2)).
If the pumps are in a large capacity, large diameter well such that each pump can be taken
out of service, and replaced or repaired without the need to interrupt operation of the
other pump(s), DOH may consider the installation equivalent to independent sources.
There should not be any significant reliability issues that independent sources would
better address (imminent threat of groundwater contamination, and high transmission
main vulnerability). Furthermore, the well design should include controls to detect a
pump failure, an auto-switch to a good pump, and an auto dialer to indicate the pump has
Multiple pumps in one well that can only be repaired or replaced by taking the source out
of service may not be considered equivalent to multiple sources. This type of installation
may still allow reduced SB volumes if the purveyor includes a plan to address repairs and
minimize downtime in the operations program for the water system (WAC 246-290-415).
In either situation, the well(s) should be easy to access for repairs and pump removal. Purveyors
should consider a service contract with a qualified repair or service entity, when appropriate, to
meet customer expectations for service.
AWWA. 1999. Design and Construction of Small Water Systems, 2
Edition, American Water
Works Association, Denver, CO.
Great Lakes-Upper Mississippi River Board of State and Provincial Public Health and
Environmental Managers. 2007. Ten State Standards - Recommended Standards for
Water Works. Health Education Service, Albany, NY.
Kippin, S. J., J.R. Pet, J.S. Marshall, and J.M. Marshall. 2001. Water Quality Impacts from
Blending Multiple Water Types, AWWA Research Foundation, Denver, CO.