Did You Know?

Everyone lives in a watershed!

A watershed is a drainage basin that collects precipitation which eventually drains to a common water body (e.g., stream, lake, wetland). Precipitation in a watershed may also sink into the earth to become groundwater. Depending on where you live, most of the water you drink comes from watersheds!






What is a Watershed?

A watershed is the area of land where all of the water that is under it or drains off of it goes into the same place. John Wesley Powell, scientist geographer, put it best when he said that a watershed is:

"that area of land, a bounded hydrologic system, within which all living things are inextricably linked by their common water course and where, as humans settled, simple logic demanded that they become part of a community."


Watersheds come in all shapes and sizes. They cross county, state, and national boundaries. In the continental US, there are 2,110 watersheds; including Hawaii, Alaska, and Puerto Rico, there are 2,267 watersheds.



What is a Watershed Approach?

A watershed approach is the most effective framework to address today's water resource challenges. Watersheds supply drinking water, provide recreation and respite, and sustain life. Nationally, more than $450 billion in food and fiber, manufactured goods, and tourism depends on clean water and healthy watersheds.

A Watershed Approach:

What do we mean by "water quality"?

Water quality can be thought of as a measure of the suitability of water for a particular use based on selected physical, chemical, and biological characteristics. To determine water quality, scientists first measure and analyze characteristics of the water such as temperature, dissolved mineral content, and number of bacteria. Selected characteristics are then compared to numeric standards and guidelines to decide if the water is suitable for a particular use. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/

How is water quality measured?

Some aspects of water quality can be determined right in the stream or at the well. These include temperature, acidity (pH), dissolved oxygen, and electrical conductance (an indirect indicator of dissolved minerals in the water). Analyses of individual chemicals generally are done at a laboratory. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/



Why do we have water-quality standards and guidelines?

Standards and guidelines are established to protect water for designated uses such as drinking, recreation, agricultural irrigation, or protection and maintenance of aquatic life. The U.S. Environmental Protection Agency (USEPA) and the States are responsible for establishing the standards for constituents in water that protect agriculture, drinking water, and aquatic life, including fish, and fish-eating wildlife such as birds. CDPHE, Regulation 32


How do natural processes affect water quality?

Natural water quality varies from place to place, with the seasons, with climate, land use, and with the types of soils and rocks through which water moves. When water from rain or snow moves over the land and through the ground, the water may dissolve minerals in rocks and soil, percolate through organic material such as roots and leaves, and react with algae, bacteria, and other microscopic organisms. Water may also carry plant debris and sand, silt, and clay to rivers and streams making the water appear “muddy” or turbid. When water evaporates from lakes and streams, dissolved minerals are more concentrated in the water that remains. Each of these natural processes changes the water quality and potentially the water use. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/


What is naturally in the water?

The most common dissolved substances in water are minerals or salts that, as a group, are referred to as dissolved solids. Dissolved solids include common constituents such as calcium, sodium, bicarbonate, and chloride; plant nutrients such as nitrogen and phosphorus; and trace elements such as selenium, chromium, and arsenic.

In general, the common constituents are not considered harmful to human health, although some constituents can affect the taste, smell, or clarity of water. Plant nutrients and trace elements in water can be harmful to human health and aquatic life if they exceed standards or guidelines.

Dissolved gases such as oxygen and radon are common in natural waters. Adequate oxygen levels in water are a necessity for fish and other aquatic life. Radon gas can be a threat to human health when it exceeds drinking-water standards. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/


How do human activities affect water quality in the watershed?

Urban and industrial development, farming, mining, combustion of fossil fuels, stream-channel alteration, animal-feeding operations, and other human activities can change the quality of natural waters (point and nonpoint sources of pollution). As an example of the effects of human activities on water quality, consider nitrogen and phosphorus fertilizers that are applied to crops and lawns. These plant nutrients can be dissolved easily in rainwater or snowmelt runoff. Excess nutrients carried to streams and lakes encourage abundant growth of algae, which leads to low oxygen in the water and the possibility of fish kills. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/


What is non-point source (NPS) pollution?

Pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides.
In the Purgatoire watershed various nonpoint sources of pollution affect water quality such as abandoned mine adits, agricultural activities, wildfire disturbance areas, runoff from residential and industrial development.


What is point-source pollution?

Point source pollution is water pollution coming from a single point of discharge, such as a discernible outflow pipe. All point sources are issued a discharge permit as part of the Colorado Discharge Permit System (CDPS) within the Colorado Department of Public Health and Environment (CDPHE), Water Quality Control Division.
In the Purgatoire watershed, examples of point sources with discharge permits include the Town of Cokedale municipal wastewater treatment facility, CBM produced water discharges, and the New Elk coal mine.

What are the water quality standards in the Purgatoire and the tributary watershed canyons?

The Colorado Water Quality Control Commission (WQCC) establishes water quality standards and designates classified uses (i.e. agricultural, aquatic life, domestic, industrial, and recreation) in all waters in Colorado…rivers, streams, lakes, and reservoirs. Water quality standards and classified uses are typically re-evaluated by the WQCC every three years during the Rulemaking Hearing for Regulation No. 32 Classifications and numeric standards for Arkansas River Basin. (http://www.cdphe.state.co.us/regulations/wqccregs/32_2012(01).pdf). Water quality standards and classified uses in the Purgatoire River watershed varies by river segment as shown on page 21 of the attached table. (http://www.cdphe.state.co.us/regulations/wqccregs/32_2012(01)tables.pdf)

River segments in the Purgatoire River basin (of the Lower Arkansas River basin) is as follows;

Water quality standards for selected metals are calculated based on hardness measurements (measured as calcium carbonate in mg/L) taken in the water during Tetra Tech's monthly monitoring. Water quality standards for the Purgatoire River, Segment 5a, including metal concentrations which are calculated based on hardness values are provided below:

July Water Quality Standards


What are the Method Detection Limits (MDL) for each analyte sampled by Tetra Tech?

The table below summarizes the detection limits, or minimum concentration of a particular constituent, that can be determined by a single measurement with a stated confidence level by our analytical laboratory, ACZ.

MDL-Water Qualtiy Standards

What are definitions for some of the water terms used by the Tetra Tech team in studying and analyzing water in the watershed?

The USGS provides an excellent glossary of water-related terms that might help you understand our site better. It is compiled from a number of sources and should not be considered an "official" U.S. Geological Survey water glossary. http://ga.water.usgs.gov/edu/dictionary.html#A

USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/


What is river "stage" and does it tell you how much water is flowing in a stream?

Not directly. You cannot say that because a stream rises (doubles) from a 10-foot stage to a 20-foot stage that the amount of water flowing also doubles. Think of a cereal bowl with a rounded bottom. Pour one inch of milk in it. It doesn't take much milk to make it up to the one inch level because the bowl is least wide near the bottom. Now, pour in milk until it is two inches deep -- it takes a lot more milk than it did to fill the first inch because the bowl gets wider as you go up. The same thing happens in a stream -- the stream banks will generally be narrower at the bottom and tend to widen as you go up the bank. So, the amount of water flowing in a stream might double when the stage rises from 1 to 2 feet of stage, but then it might quadruple when it goes from 3 to 4 feet. This graphic helps to illustrate:



To find out how much water is flowing in a stream or river, personnel have to go out and make a "discharge measurement." The term "discharge" refers to how much water is flowing, and discharge is usually expressed in "cubic feet per second" (think of a cube of water one foot on a side, and how many of those move past a point in one second). To do this, we often have to go out and stand in the creek, measure the depth and how fast the water is moving at many places across the creek. By doing this many, many times, and at many stream stages, over the years we can develop a relation between stream stage and discharge. Stream stages are not always cooperative, so it is not uncommon for someone to have to go measure a stream in freezing or rainy conditions! Also, the stream can be uncooperative in that it changes -- a big storm may come along and scour out bottom material of a creek, or lodge a big log sideways in the creek, or sometimes do both at the same time. These kind of changes result in changes in the relation between stage and discharge. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/


How is streamflow measured?

The two most fundamental items of hydrologic information about a river are stage, which is water depth above some arbitrary datum, commonly measured in feet, and flow or discharge, which is the total volume of water that flows past a point on the river for some period of time, usually measured in cubic feet per second or gallons per minute. These two key factors are measured at a location on the river called a stream-gaging station.

By using automated equipment in the gaging station, river stage can be continuously monitored and reported to an accuracy of approximately 1/8 of an inch. Linking battery-powered stage recorders with satellite radios enables transmission of stage data to computers. In this way, hydrologists know the river stage at remote sites and how fast the water is rising or falling.

It is much more difficult to measure river discharge accurately and continuously. As a matter of practicality, discharge is usually estimated from pre-established stage/discharge relations, or rating curves. The rating curves are constructed by field personnel who periodically visit the gaging station to measure river discharge. Tetra Tech field personnel routinely (monthly) conduct streamflow measurements during various flow conditions to measure river discharge and to calibrate the rating curve that is established. By using an up-to-date stage/discharge rating and a river-stage reading, an accurate estimate of the river discharge (measured in cubic feet per second) can be produced. However, changes in river cross sections that result from the scour or deposition of sediment or changes in streambed and bank roughness can alter the stage/discharge relation. Such changes are particularly prevalent during floods. Occasionally, changes are so severe as to require development of a new stage/discharge rating; as a result of a major flooding or snowmelt runoff. Thus, even after a stage/discharge rating is well established, additional discharge measurements are required periodically to detect and track changes and to update the rating. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/


What is provisional data?

Data from real time streamflow gages are relayed to the website through an Iridium Satellite data-collection system. Data are transmitted hourly from each station and are loaded onto the computer system database.
Real time data available on this website are provisional data that have not been reviewed or edited. These data may be subject to significant change and are not citeable until reviewed and approved by Tetra Tech. Real time data may be changed after review because the stage-discharge relationship or water quality probes may have been affected by:

Data are reviewed periodically to ensure accuracy. Each station record is considered provisional until the data are published. The data are usually published. The data are published annually.

Data users are cautioned to consider carefully the provisional nature of the information before using it for decisions that concern personal or public safety or the conduct of business that involves substantial monetary or operational consequences.

Information concerning the accuracy and appropriate uses of these data or concerning other hydrologic data may be obtained by contacting the individual listed on the Contact Us page. USGS, FS-027-01, March 2001, http://pubs.usgs.gov/fs/fs-027-01/


What are the objectives of the Purgatoire Watershed Monitoring Program?

The six objectives of the watershed monitoring program are:

  1. Provide water quality data to more fully understand and evaluate CBM influences on surface water quality and loading to tributaries and ultimately, the Purgatoire River both upstream and downstream of Trinidad Lake.

  2. Provide continued hydrologic and surface water quality data for the evaluation of the upper Purgatoire River and associated tributaries throughout various flow regimes.

  3. Evaluate chemical loads, trends in the concentrations, and assimilative capacity to develop management scenarios, creative options and control strategies to achieve permit compliance.

  4. Allow a comprehensive, site-wide comparison of water quality constituents of concern to applicable permit limits and WQCC water quality standards.

  5. Understand sodium adsorption ratio (SAR) and electrical conductivity (EC) relationship in the watershed as it relates to irrigated agriculture and classified uses.

  6. Provide a scientific and technical basis to support permitting decisions and water management options that could be presented to the Water Quality Control Division (WQCD) or regulatory options that could be introduced to the Water Quality Control Commission (WQCC) at a hearing for the Arkansas River basin in June 2013.

What is being tested in the Purgatoire River Basin?

The Purgatoire River Watershed is influenced by many point and non point sources, including coal bed methane (CBM) operations. Currently, the CBM operators in this watershed have approximately 3,500 CBM extraction wells with ability to discharge up to approximately 10 million gallons per day (MGD) (equivalent to 15.16 cubic feet per second (cfs) or 11,300 acre-feet/year) of produced water in the basin. The testing and data collection of the site-wide monitoring program provides relevant information to support permitting decisions and regulatory options that could be introduced to the Colorado Water Quality Control Commission, coupled with adherence of state regulatory requirements for water quality.


How timely is the data?

Interested parties will be able to review provisional water data via 9 continuous satellite monitoring stations near real-time. Continuous monitoring data is collected at 15-minute intervals.

Monthly provisional data is collected at 25 locations will measure pH, specific conductance, temperature, flow, boron, calcium, copper, iron, lead, magnesium, selenium, sodium, zinc, alkalinity, chloride, sulfur, total suspended solids and total dissolved solids.


When is the monitoring program in effect?

Tetra Tech personnel will start implementing the monitoring program and begin surface water sampling in April 2010, with appropriate access agreements being addressed in advance.  The initial year of the surface water monitoring program will be from April 2010 through December 31, 2010.  The subsequent year’s monitoring program will begin on January 1, 2011 and continue through December 31, 2011. 

Will there be public meetings?

Periodic meetings with the operators, stakeholders, and regulators will be held to discuss the project.  This website will contain public meeting information as it becomes available.