Well #4 “getting a rest” to ameliorate manganese problem.

Well #4 is offline and will remain so until demand gets so high that Well #6 can no longer supply the whole system.  Well #4 generally produces water containing 50 ppm of manganese, which equals the secondary standard for that contaminant.  High manganese concentrations tend to give the water a brown color and a metallic taste and may cause black stains.  More information here. Manganese tends to accumulate at the dead ends of mains and can be managed by periodic flushing, but Crestview is now trying to lower the concentrations in pumped water by letting Well #4 “rest” so that it pulls more water from higher strata and less from the deeper zones that are believed to have higher manganese concentrations.

When the pump was lowered in Well #4 and it came back online in June 2022, three assays of manganese in June were 80 ppm, 80 ppm, and 60 ppm, but by September 2022, the concentration had stabilized at 50 ppm. Table here. For comparison, water produced by Well #6 consistently contains only 40 ppm of manganese.

In response to questions from the Board on January 23, Superintendent McAdoo said that Well #6 could supply the whole system for a larger part of the year if it were run more hours. It could, if necessary, be run from midnight to 4:00 p.m. without paying a higher rate for electricity.  However, running Well #6 longer hours would create a risk that it would draw in water with higher manganese concentrations.

For further context, Well #5 had such high concentrations of manganese and iron (Crestview Watch does not know what those concentrations were) that a Treatment Plant was installed at the location of Well #5 and Reservoir 3 to remove those contaminants.  Apparently, treatment did not work well enough, and Well #6 was drilled to replace Well #5 (which has been idle since).  Crestview thought high manganese and iron concentrations were likely to be found at the 191 Alviso location of proposed Well #7, and 1,600 feet of new transfer main was included in the initial design in order to get water directly to the Treatment Plant. In the continuing evaluation of alternative locations for Well #7, at least two other sites are thought likely to produce water high enough in manganese and iron to require treatment. Crestview has estimated that it would cost approximately $1,000,000 to restart the Treatment Plant.

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