Water Supply Characteristics

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.

Geological Survey
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
Wells 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.