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

The Stormwater Quality Program, Water Quality and Environmental Services, City of Boulder, conducts water quality monitoring to assess the impacts of point and non-point sources of pollutants to Boulder Creek and to help develop mitigation measures to reduce these impacts. To understand the threats which Boulder's surface waters are facing, it is necessary to examine how the resources are changing over time. Accurate information on the status and trends of the environment can help identify source controls. The Stormwater Quality Program collects monthly water quality samples from the North Boulder Creek Falls to the confluence of Boulder Creek with Coal Creek.

Stormwater 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 ° C. The remaining bottles are cleaned in a dishwasher, which involves a hot water and detergent wash, steam cycle, and deionized water rinse. Bottles used for metals are also soaked in 3% nitric acid (HNO 3 ) and then rinsed with deionized water three times. Bottles are then air-dried.

Sample Collection:

Samples are collected in accordance with procedures outlined in Standard Methods for the Examination of Water and Wastewater, 20th Edition (section 1060).

The following describes general collection procedures for grab samples:

In the field, sample bottles are rinsed two times with water being collected, unless a preservative or dechlorinating agent has been added to bottle prior to use. Various types of sample bottles are used depending on constituent being tested for and method of analysis being used.

Samples are taken from mid-channel or the area in the channel which best represents the flow. Sample bottles are submerged to approximately 60% of the water depth and water is allowed to flow into them. The sample is capped and shaken. One to two inches of space is left in the bottle to allow for thermal expansion (unless sample analysis requires that no air space be left).

Sample preservative is added after sample collection as prescribed by each analytical method. Metals samples are filtered in the laboratory before being acidified.

Sample labels are completed and samples are placed in cooler with blue ice. Samples are transported to laboratory and placed in refrigerator for storage at 4 ° C

Field blanks are used for every sampling event. Field blanks are filled with deionized water and are treated in the same manner as other sample bottles. Duplicate samples are also collected for each sampling event.

Field Parameters:

Field instruments used for pH and Dissolved Oxygen (DO) are ion-selective probes. The Orion Model 1230 pH/DO/Temp is used to measure these parameters. pH is calibrated using pH buffers 7 and 10 in the wastewater laboratory before each sample event. The probe has automatic temperature compensation for temperature-corrected buffer values. A calibration sleeve is used to calibrate DO in the wastewater laboratory before each sample event. The instrument automatically measures and compensates for temperature and total atmospheric pressure.

The Orion Model 130 conductivity meter is used for Specific Conductance (SC) and water temperature. The probe is calibrated before each sample event with a potassium chloride (KCl) solution of 1412 micromhos/cm at 25 ° C.

The Orion Model 840 DO meter and the Orion Model 140 conductivity meter are used as backups if a problem with the main meters occurs in the field.

Flow velocity is measured using the Marsh-McBirney Flo-Mate 2000 portable flowmeter. USGS midsection methods, as described in the Water Measurement Manual, are followed. Calibration is performed at the factory.

Laboratory Analysis:

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 using Standard Methods 4500-NH 3 B and 4500-NH 3 C. Both the ammonium ion (NH 4 + ) and unionized ammonia (NH 3 ) are included in the measurement. Sodium borate buffer is added to the sample, and the pH of the sample is adjusted to 9.5 with sodium hydroxide (NaOH). The sample is then distilled into a flask that contains a boric acid/color indicator solution. The distillation separates ammonia (which goes into the distillate) from organic nitrogen compounds. The distillate is titrated with sulfuric acid (H 2 SO 4 ) until the solution turns a pale lavender. The volume of acid required to change the color of the sample reflects the ammonia concentration of the sample.

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 8039 (high 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. This salt then couples to gentisic acid to form an ambered-colored product. The amber color is then analyzed with a spectrophotometer; the more intense the amber, the more nitrate+nitrite in the sample. The detection limit for this method is approximately 0.1 mg/L . The analysis is performed on filtered samples to eliminate turbidity interferences.

Total Phosphorus is measured using a Hach DR4000 spectrophotometer, Method 8190. In this method, phosphorus present in organic and condensed forms is converted to reactive orthophosphate before analysis. Sulfuric acid (H 2 SO 4 ) and potassium persulfate (K 2 S 2 O 8 ) are added to 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 orthophosphate. After boiling, the sample is cooled, and sodium hydroxide (NaOH) is added, along with a solution of ascorbic acid and molybdate reagent. The sample turns blue, with the intensity of the blue proportional to the orthophosophate concentration.

Orthophosphorus is measured using a Hach DR4000 spectrophotometer, Method 8114. This method is based on Standard Method 4500-P.C. Molybdovanadate reagent is added to the sample. The molybdate reacts in the acid with the orthophosphate to form a phosphomolybdate complex. In the presence of vanadium, yellow vanadomolybdophosphoric acid is formed. The yellow color is then analyzed with a spectrophotometer; the more intense the yellow, the more orthophosphate in the sample. The detection limit for this method is approximately 0.09 mg/L PO 4 /L.


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