AWWA DSS54636

The City of San Antonio is the largest city in the United States that is solely dependent upon groundwater as its drinking water source. Studies have indicated that the current withdrawals from the Edward's Aquifer are depleting this source, which means that the City of San Antonio must find alternative water supplies to reduce existing water use from the aquifers, as well as to provide for future growth. Water quality problems can occur when new water sources are introduced to an existing water system due to changes in baseline water chemistry and changes in system hydraulics and flow patterns. This project examines one potential problem associated with changing baseline water chemistry: the release of corrosion products and scales that are currently in the distribution system. When the baseline water chemistry is modified as with the introduction of water from a new source, the equilibrium is upset and scales and corrosion products respond to meet a new equilibrium and can react in a release of material causing red water episodes. Red or brown water typically develops from the release of iron corrosion products from older iron piping. It is important to successfully manage re-equilibration to prevent scale or corrosion product release that significantly impares water quality. The purpose of the iron release and re-equilibration (IRR) portion of the integration study is to determine the potential for aesthetic degradation resulting from water chemistry changes in older distribution system areas having a higher prevalence of unlined cast and/or ductile iron distribution mains, or older homes plumbed with galvanized iron pipe. The IRR uses pipe loop testing with specimens of aged galvanized piping from these areas. Results of the testing program will be used to determine appropriate chemical treatment and/or distribution water chemistry modifications that will ensure the stability of existing iron scales and the minimization of potential red/brown water problems. This paper presents the methodology and results of the pilot-scale iron release testing including the impact of varying hydraulic flow regimes, stagnation conditions, source water blend ratios and corrosion control strategies imposed on the pipe loops to assess the impact of different operational and treatment variables. Includes reference, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

09/01/2001

Number of Pages:

17

File Size:

1 file , 450 KB