Maintain a High Quality of Water
Regularly monitor 10 critical parameters for water quality below the Nichols Reservoir and/or at the water treatment plant.
Critical parameters that require regular analysis for water quality include a total of 10 parameters, and monitoring will occur below the Nichols Reservoir or at the water treatment plant.
Total Organic Carbon (TOC) and Dissolved Organic Carbon (DOC)
TOC and DOC are important to water treatment operators because of the potential for organic carbon to form trihalomethanes (THMs) as a disinfection byproduct during chlorination. THMs are carcinogens and regulated by EPA. TOC and DOC are sampled once a month in raw water by the WTP below Nichols Reservoir as required by the EPA.
E. coli, Giardia and Cryptosporidium
E. coli, Giardia and Cryptosporidium in raw water have been sampled monthly by the WTP since April 2007 as required by the EPA Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). Monthly samples are collected at the outlet from Nichols Reservoir and submitted to a laboratory, which will continue until March 2009. Results of the sampling will determine the level of treatment required at the City WTP. If the mean concentration is less than .075 oocyst/L, then minimal treatment will be required and the two-year monthly sampling cycle will be repeated six years later (in 2015). Results to date, show very low detections of cryptosporidium.
Water temperature impacts the “metabolism, behavior and mortality of fish and other aquatic organisms” (NMED 2008). Continuous measurement of temperature is necessary to determine the maximum daily temperatures, the duration of excessive temperatures and the diurnal and seasonal fluctuations of temperature that effect aquatic life. New Mexico Water Quality Standards (184.108.40.206.B1) for temperature is less than 20 oC for aquatic cold water fisheries.
Dissolved Oxygen (DO)
Cold water aquatic species, particularly embryos and larvae, are more sensitive to dissolved oxygen concentrations than warm water species. DO concentrations need to be at least 6 mg/L for healthy aquatic systems. Because DO is impacted by temperature and elevation, the percent saturation of DO is also important and it should approach 100%. Cold water can hold more oxygen than warm water.
The water treatment plant and aquatic life are both sensitive to the pH of water. The treatment plan operators need to know the pH to adjust the alkalinity of the water to achieve good coagulation and produce stabilized water. The pH is measured continuously by the City WTP at the intake before treatment (out of Nichols Reservoir). NMED SWQ Bureau has also measured pH in Santa Fe River water in three locations, three times a year. The pH should remain between 6.6 and 8.8 (NMWQCC, 2007). Measured pH at the three sites in the Upper Watershed average 7.3, with a maximum observed at 8.7 in the fall at the inflow into McClure and a minimum of 6.1 measured several times in the spring at the wilderness boundary and at the inflow to McClure Reservoir. The low alkalinity of the water results in a lack of buffering capacity for the water which allows the pH to be unstable.
The specific conductance or electrical conductivity of water is an indicator of the total dissolved solids. It is a very inexpensive field check on water quality and could be used to indicate significant changes in water quality. EC has been recorded in the field by NMED SWQB at three sites, three times a year. EC measurements have ranged from 31 to 187 μmhos/cm in the Upper Watershed, less than the numeric criteria of 300 μmhos/cm or less (NMWQCC, 2007).
Turbidity is a principal physical characteristic of water and is an expression of the relative clarity of a liquid. It is caused by suspended matter or impurities that interfere with the clarity of the water. These impurities may include clay, silt, finely divided inorganic and organic matter, soluble colored organic compounds, and plankton and other microscopic organisms.
Clarity is important when producing drinking water for human consumption and in many manufacturing uses. Excessive turbidity, or cloudiness, in drinking water is aesthetically unappealing, and may also represent a health concern. Turbidity can provide food and shelter for pathogens. If not removed, turbidity can promote regrowth of pathogens in the distribution system, leading to waterborne disease outbreaks, which have caused significant cases of gastroenteritis throughout the United States and the world. Although turbidity is not a direct indicator of health risk, numerous studies show a strong relationship between removal of turbidity and removal of protozoa. (EPA 1999).
Alkalinity (Total Hydroxide, Carbonate, Bicarbonate)
Alkalinity is a measure of the ability of a solution to neutralize acids to the equivalence point of carbonate or bicarbonate. In affect, it is a measure of the buffering capacity of the water. Alkalinity is important to monitor for municipal water supplies because of its affect the amount of chemicals needed to achieve coagulation and also impacts the corrosion in distribution systems. Alkalinity is measured once a month by the City WTP below Nichols Reservoir.
PCBs were detected in the outfall from Nichols Reservoir on May 3, 2007 at concentrations totaling 0.235 μg/L, which is above the standard of .064 μg/L for domestic water supply and 0.014 μg/L for aquatic life and wildlife habitat. No other locations were sampled. We recommend that surface water be sampled for PCBs at the two locations above each reservoir to verify these results and determine if further assessment is necessary. If samples show no detection of PCBs, then no further sampling is recommended. If PCBs are detected, the NMED should be contacted to investigate the extent and source of contamination.