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BDD Water

Water Treatment Process

Pilot Treatment facility

pilot treatment facility

To choose the best way to treat the San Juan-Chama water diverted from the Rio Grande so that it meets all federal and state drinking water standards, the BDD team conducted a Surface Water Treatment testing program from April-October 2005. This time period allowed testing of the water during different seasons and conditions (runoff from winter snow, spring rains, summer monsoons, etc.). The program also included wide-range testing of the river water to understand the water and its makeup through the various seasons.

A pilot treatment facility evaluated many different treatment processes and chemicals. Through this testing program, tours of other treatment plants, and workshops, the team identified the best treatment process choice

Selected Treatment Process

The treatment process selected for the City/County Water Treatment Plant is a combination of Membrane Filtration with Ozone and Granulated Activated Carbon (GAC) Contactors. This treatment process will reliably produce high-quality drinking water without the operational concerns of other processes. This choice will provide good value through capital costs and was the most reliable, prudent, and robust of all options considered. This treatment process uses the best available technology for removal of radionuclide contamination.

The treatment process includes:

Water treatment schematic

one Diversion, Sediment Removal and Pumping – River water will be diverted from the Rio Grande through a five-bay, reinforced concrete structure with fish screens and cleaning systems. After the larger sand and grit particles are removed, the raw water will be pumped uphill through two booster stations approximately 11 miles to the City/County Water Treatment Plant.
two Presedimentation and Raw Water Storage – Two gunite-lined earthen basins will allow larger particles to settle to the bottom for removal. These basins, and a third storage basin, will allow for splitting and storage of a significant amount of raw water as well as blending of the water to smooth out water quality.
three Coagulation – A flash mix system will use pumped water to rapidly mix a metal salt (ferric chloride) with the raw water so that particles and organic materials can be removed in later treatment processes. This process is enhanced by the addition of ozone, a strong oxidizer.
four Flocculation – Flocculation basins will use mixers in a three-stage process to combine coagulated particles into a larger, heavier material called “floc” that is easier to settle.
five Sedimentation with Plate Settlers – Settling of heavy “floc” will occur in reinforced concrete basins to remove most of the remaining solids and organic material, which will then be dewatered and moved off-site for disposal.
six Membrane Filtration – The Membrane Filtration (MF) system will remove the remaining small suspended solids and biological elements. Under pressure, the MF will remove any Giardia, Cryptosproidium, bacteria, protozoa and suspended solids by filtering water through extremely small pores (that are not visible to the eye) in the walls of hollow fiber membranes.
seven Ozone Generating and Contacting - Remaining organic material in the water will be oxidized with ozone for removal in the downstream GAC Contactors. This process greatly reduces formation of byproducts from downstream disinfection of the water. The ozone also oxidizes taste- and odor-causing compounds to improve the taste of the water.
eight GAC Contactors – The next step in the water treatment process is to force the water through five 40-foot-long, 12-foot-diameter pressurized tanks containing granular activated carbon (GAC). The oxidized organic materials and other compounds are absorbed onto the GAC to “polish” the drinking water.
nine Final Treatment Steps - After it is treated and chlorine is added to it, the water will be stored in two Finished Water Tanks at the City/County Water Treatment Plant. Each tank will be able to hold as much as four million gallons of water. Sodium hypochlorite (chlorine) will again be added to the water as it is pumped through two pump stations into the distribution systems. The chlorine provides further disinfection of the water and helps it remain safe in the distribution systems.