City of Boulder/USGS Water Quality Monitoring
City of Boulder Drinking
Water Sampling Methods

The Drinking Water Program, Water Quality and Environmental Services, City of Boulder, conducts sampling of waters that are sources of drinking water for the City of Boulder. These samples are collected to characterize the quality of water used by the City of Boulder. This characterization includes assessing seasonal trends, detecting any possible contaminants that may have entered the water, and identifying the source of any contaminants. The Drinking Water Program collects monthly water quality samples from locations such as the Lakewood Reservoir, Barker Reservoir, Middle Boulder Creek, and Boulder Reservoir.

Drinking Water Quality Sampling Procedures

Sample Bottles:

TOC bottles are obtained from the USGS, where the bottles are washed with hot, soapy water, rinsed with tap and distilled water, and burned for 8 hours at 250 degrees C. For the remaining bottles, each set of sample bottles is cleaned and reused for one particular sample site. After sampling, sample bottles are rinsed with tap water immediately after the sample has been analyzed. All sample bottles except those used for chlorophyll, metals, and bacteria are soaked for at least one hour in a 5% hydrochloric acid (HCl) bath. These bottles are then rinsed twice with tap water and twice with deionized water and allowed to air dry. Chlorophyll abottles are rinsed with tap water only and allowed to air dry. Metals bottles are soaked in a 3% nitric acid (HNO3) bath for at least one hour. Metals bottles are than rinsed in the same manner as the HCl-washed bottles. The day prior to sampling, all sample bottles except those used for bacteria are half-filled with deionized water and packed in sealed ziploc bags.

Sample Collection and Treatment:

All samples except Nederland effluent and samples from the water treatment plant taps are composite samples. Streams samples are vertically-, horizontally-, and time-composited. HCl-washed sample churns are used for compositing samples. All sample bottles are filled from the same aliquot of water. Reservoir top samples are composited from the photic zone using a Van Dorn instrument.   Samples are repacked in the original ziploc bag and placed in coolers containing ice. Samples requiring filtration are filtered immediately upon arrival back at the lab. Samples are then acid-preserved and/or refrigerated, as required.

One replicate sample is collected for each sampling event. For field blanks, laboratory millipore water is transported to the field. Clean field equipment is used to fill a clean churn with this blank water. All field blank bottles are then filled from this blank water churn.

Field Parameters:

Water Temperature is analyzed with a YSI 600XL multi probeYSI 600XL multi probe. The temperature probe is checked annually.

Dissolved Oxygen is analyzed with a YSI 600XL multi probe. Calibrations are conducted in the field at the sample site with a moist-air saturated bottle.

Specific Conductance is analyzed with a YSI 600XL multi probe. The probe is calibrated in the drinking water laboratory the day of sampling. A potassium chloride solution of 1412 micromhos/cm at 25 ° C is used in the calibration. Standards are replaced at least monthly.

pH is analyzed with a YSI 600XL multi probe. The probe is calibrated with pH 7 and 10 buffers in the drinking water laboratory the day of sampling. Buffers are replaced at least monthly.

Laboratory Analysis:

For colorimetric analyses (nitrate+nitrite, sulfate, orthophosphorus, and total phosphorus), all spectrophotometer cuvettes are HCl-washed and/or cleaned with soap.   The instrument is zeroed with the sample or with lab millipore water depending on the procedure. Two standards are run, and bracket the sample value. New standards are prepared monthly. New high- and low-range 5 point curves are constructed for the Genesis spectrophotometer when necessary.

Alkalinity is measured using Standard Method 2320B (American Public Health Association, 1998). The sample is stirred, and temperature and pH are monitored, as 0.02N sulfuric acid (H 2 SO 4 ) is slowly added to the sample. The amount of acid necessary to bring the sample pH down to 4.5 is proportional to the total alkalinity in the sample. This method assumes that the entire alkalinity consists of bicarbonate, carbonate, and/or hydroxide.

Ammonia is measured by the wastewater laboratory.

Hardness is measured using Standard Method 2340C. A small amount of dye is added to the sample, and buffer solution is added until the pH of the sample reaches 10. If calcium and magnesium are present in the sample, the sample turns red. Ethylenediaminetetraacetic acid (EDTA) is then added until the sample turns blue. The amount of EDTA required to turn the sample blue represents the hardness of the sample.

Nitrate+Nitrite is measured using a Hach DR2000 spectrophotometer, Method 8192 (low range cadmium reduction). Cadmium metal reduces nitrates present in the sample to nitrites. The nitrite ion reacts in an acidic medium with sulfanilic acid to form an intermediate diazonium salt which couples to chromotropic acid to form a pink-colored product. The pink color is then analyzed with a spectrophotometer; the more intense the pink, the more nitrate+nitrite in the sample. The detection limit for this method is approximately 0.01 mg/L.

Total Phosphorus is measured using Standard Method 4500-P B.5 and 4500-P E. In this method, phosphorus present in organic and condensed forms is converted to reactive orthophosphate before analysis. Sulfuric acid (H 2 SO 4 ), and ammonium persulfate ([NH 4 ] 2 S 2 O 8 ) are added to 50 mL of the sample, and the sample is boiled. The acid and heating causes hydrolysis of condensed inorganic forms of phosphorus. The acid, heating, and persulfate causes organic phosphorous to convert to orthophosphates. After boiling down to approximately 10 mls, the sample is cooled and the phenolphthalein indicator is added. The sample pH is adjusted to 8.3 using sodium hydroxide (NaOH) and sulfuric acid (H 2 SO 4 ). The sample is then brought back up to volume and analyzed for orthophosporus as discussed below.

Orthophosphorus is measured using Standard Method 4500-P E. Sulfuric acid (H 2 SO 4 ), potassium antimonyl tatrate, ammonium molybdate, and ascorbic acid are added to the sample. The potassium antimonyl tatrate and ammonium molybdate react in the acid with the orthophosphate to form phosphomolybdic acid. The phosphomolybdic acid is then reduced to a blue color by the ascorbic acid. The blue color is then analyzed with a spectrophotometer; the darker the blue, the more orthophosphate in the sample. The detection limit for this method is approximately 0.002 mg/L P.


American Public Health Association. 1998. "Standard Methods for the Examination of Water and Wastewater." 20th edition.

Select here for general information about these water quality parameters.

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Last Page Update - Friday December 23, 2005