Old Mill Spring

Also known as Sunken Gardens, Old Mill spring is located east of the pool, and is currently fenced to protect the Barton Springs salamander. Water flows into the pool shown here through multiple upwellings that are difficult to discern.

Spring Discharge

The average flow is about 5 cubic feet per second (2,250 gallons per minute).

Spring Water Chemistry

The chemistry of Old Mill Spring water (as well as the three other springs) is predominately a calcium bicarbonate water with low concentrations of dissolved solids. In general, Old Mill Springs has higher concentrations of sodium, chloride, and sulfate than the other three springs.

Spring Water Quality

The spring water quality is assessed by analyzing concentrations of chemical constituents such as major ions, nutrients, and some of the many different contaminants often found in urban settings. These contaminants include pesticides, volatile organic compounds, and nutrients. At Old Mill Springs, samples for analysis of major ions and nutrients in baseflow are being collected every three weeks, and samples for analysis of contaminants are being collected quarterly. Click here for more detailed information on the contaminants investigated.