Water solutions at an affordable cost

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By Pete Sheehey

Second of a series
One of the major issues in this town is water: do we have enough to keep this a green community, at an affordable cost?
Contamination Threats and Mitigation
Laboratory operations since the 1940s resulted in a wide array of chemical releases, often in effluent discharged from wastewater treatment facilities. Many millions of dollars have been spent to monitor and remediate the environmental contamination caused.
Reactive contaminants, including plutonium and other radionuclides, tend to adhere to solid surfaces, so they usually have not moved very far in groundwater. In fact, wastewater effluent (now treated to strict standards to prevent further contamination) is used to irrigate vegetation holding soil in place to keep previously deposited surface contamination from spreading.
Non-reactive contaminants, including hexavalent chromium, tritium, nitrate and explosives components perchlorate and RDX, have traveled farther in our groundwater, in some cases reaching portions of our aquifer. The presence of these contaminants above naturally occurring levels has not been detected in our water supply wells, but unless carefully monitored and properly remediated, they could threaten our water supply.
The main thrust of present mitigation work is to try to remove the contaminants from the aquifer before they reach our supply wells. The most serious threat today is hexavalent chromium (Cr+6), which was discharged for many years in cooling tower water containing potassium dichromate to prevent scale buildup. The use of potassium dichromate was discontinued, and the Los Alamos National Laboratory has made significant investments in contamination-preventing and water-saving technology. The LANL Sanitary Effluent Reclamation Facility (SERF) purifies wastewater so that it can be used in cooling towers multiple times.
A plume of water containing Cr+6 exists within half a mile of one of our Pajarito supply wells (PM-3), which are the biggest producers in the county’s water system. In a presentation to the State Legislature’s Radioactive and Hazardous Materials Committee (LA-UR-14-25531, July 23, 2014), LANL described plans to begin pumping water from this part of the aquifer and treating it to remove the Cr+6. In the first year, this could involve pumping as much as 400 ac-ft/yr. If necessary, pumping could go up to as much as 1,190 ac-ft/yr within three years. This rate of pumping could continue for years, depending upon the measured Cr+6 removal results.
“Pump and treat” is one approach being pursued to remove Cr+6. A second approach planned is “in-place treatment wells,” in which substances are introduced to contaminated groundwater in the aquifer to reduce Cr+6: chemical reducing conditions, produced by chemical or biological means, can transform Cr+6 to the naturally occurring (and non-health-threatening) Cr+3 form. Wetlands irrigated by clean effluent discharge create conditions in the soil favoring this type of removal of Cr+6 remaining in the surface water.