The Terrace Heights Water System includes 6 supply wells. Wells 2, 4, 5
and 6 draw from the Ellensburg formation, which consists of
semi-consolidated deposits of clay, silt, sand and gravel. Well 3 draws
from the Saddle Mountain formation in the Yakima Basalt aquifer, which
underlies the Ellensburg formation, and Well 1 draws from a perched
aquifer on Yakima Ridge. Information regarding each well, including
capacity, was included in Chapter 2.
The U.S. Geological
Survey is conducting a detailed study of the ground water sources in the
Yakima River Basin. According to USGS, preliminary results of the study
indicate water levels are relatively stable in the Terrace Heights area
(Township 13 Range 19). USGS’s data shows a few wells with 5’ of
decline. East of Terrace Heights in the Moxee Valley, declines in the
ground water level increase. Township 13 Range 20, which is 6 miles to
the east of Terrace Heights, has some wells with declines of 40 to
50-feet in the Saddle Mountain and Wanapum aquifers. In Township 13
Range 21, the declines are worse. According to USGS, the declines are
primarily in the basalt and deeper Ellensburg wells (wells over 1000’),
although they also claim the bottom of the Ellensburg can be course
grain and very productive. The upper Ellensburg formations are recharged
in part by irrigation and irrigation canals and are not experiencing
the declines seen in the basalt wells.
According to USGS,
water levels decline in the basalts during drought years due to
increased pumping from irrigators with junior Water Resources Division
rights. During drought years, irrigators with junior Water Resources
Division rights resort to using their groundwater wells.
Wells to the North
to the north along Yakima Ridge are also experiencing declines. This is
said to be due to the wells being located along the anticline of the
ridge rather along the syncline of the valley. The Terrace Heights Well Number 2 is an example of this. This well has experienced 50 feet of decline since
it was drilled. In the last 10-years, the decline has stabilized.
Seasonal variations do not have an impact on the ability of the Terrace Heights wells to meet demands.