In addition to sources in the Green River watershed, we own 24 wells in and around Tacoma. Our wells pump water from aquifers, which are underground layers of water, saturated sand and gravel. This water comes from local rainfall.
The majority of the groundwater we use comes from wells in the South Tacoma wellfield. The South Tacoma wells pump from very productive underground aquifers that stretch from the north of the Nalley Valley all the way to Lakewood.
We first began developing the wells in South Tacoma in the early 1900s and now have 14 wells in this wellfield. Our wells can pump about 60 million gallons per day. During the summer months, the wells help meet peak summer water needs.
Not only have these wells been critical to the past and present of our water supply, they are critical to the future drinking water supply.
Groundwater typically supplies about 10% of Tacoma's water in the summer and supplements the supply from the Green River at other times of the year. Tacoma Water samples its drinking water wells for bacteria and for traces of more than 150 different metals and chemicals. Tacoma Water also samples numerous dedicated monitoring wells.
The homes of 30,000 people, as well as hundreds of businesses, are located above the underground aquifer that supplies the wells in the South Tacoma wellfield. Many of these businesses use, handle and store chemicals that can contaminate groundwater. In addition, most homes have numerous household chemicals, pesticides, and fertilizers that can contaminate groundwater if they are disposed of or applied improperly.
If a groundwater well is contaminated, we must either treat the water or replace the well so that enough water would continue to be available for customers. Both of those options are expensive. Preventing contamination is much less expensive and more effective than fixing a problem after it has occurred. We work hard to educate both residents and businesses who are located in areas above our drinking water aquifers about ways to prevent contamination of our drinking water.