City of Union Gap Wellhead Protection Plan

The City of Union Gap is located in Yakima County at the foot of the Upper Yakima Valley in central Washington. The City limits extend from the gap formed by the Yakima River in Ahtanum Ridge northerly to the City of Yakima, and from the Yakima River on the east to principally 16th Avenue on the west. The City has historically owned and operated 3 wells:
  • Well Number 1 was drilled in 1936 and pumps 75 gallons per minute.
  • Well Number 2 was abandoned in the 1950s and is currently used to monitor groundwater levels.
  • Well Number 3 was drilled in 1949 and pumps 460 gallons per minute.
  • Well Number 4 was drilled in 1959 and pumps 1,235 gallons per minute.
The City has total certified water rights in the amount of 2,664 acre-feet. The City’s sources have historically provided high quality water.

Wellhead Protection Area Delineations
The City's wellhead protection areas (WHPA) were delineated using an analytical model. The following table summarizes the acreage covered by each WHPA.

Analytical Model Area (Acres)

Source 6-Month 1-Year 5-Year 10-Year
Wellhead Number 1
 2.4 4.0 18.5 80.2
Wellhead Number 2
 4.0 7.8 43.5 99.4
Wellhead Number 3
 7.8 14.4 66.4 136.8

Inventory of Potential Contamination Sources


After delineating the WHPAs associated with the City’s wells, an inventory of existing and potential sources of groundwater contamination (PDF) was compiled and mapped. High risk potential contamination sources located near the City's wells include underground storage tanks, leaking underground storage tanks, confirmed or suspected contamination sites, hazardous waste handlers, high risk businesses, and agricultural land which may be susceptible to pesticide use.

Contingency Plan


The City's contingency plan consists of the following components:
  • Susceptibility Assessments: The Washington State Department of Health (DOH) has ranked Well Number 1 as having a low susceptibility to contamination and Well Number 3 and Number 4 as having a moderate risk to contamination.
  • Source Deficiencies: The City can currently meet the existing system maximum day demand with all sources in service as required by the DOH, but will need an additional 200 GPM in order to support the next 20 years of projected growth. However, if any of the City's wells becomes contaminated, this deficiency will increase. The City plans to drill a well in the next 6 years to provide for additional source redundancy and source capacity.
  • Emergency Response: The City has developed an emergency response plan that includes an emergency call-up list and response procedures for spills, fires, and water supply contamination.
  • Short-Term and Long-Term Water Supplies: Because the City of Union Gap has two existing interties with the City of Yakima, these represent the most appropriate short-term alternative water supply in an emergency situation. New source development, further use of the inter-tie, and groundwater remediation are the most appropriate long-term alternatives.

Local Management Plan


Local management efforts adopted by the City include:
  • Posting of street signs at wellhead protection area boundaries
  • An annual school seminar program to promote wellhead protection and water education
  • Distribution of literature
  • Notification of residences and businesses within the City's wellhead protection areas
Review the Regional Management Plan page for more information.