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Water: Nonpoint Source Success Stories

Colorado (Section 319I - 1994)

Colorado has established a nonpoint source pollution task force to develop and implement best management practices throughout the state. Its goal is to design watershed projects that balance nonpoint source and point source treatments to achieve water quality standards in an urban and semirural environment.

Boulder Creek Furnishes Laboratory for NPS Treatment

The Boulder Creek Enhancement Project, designed to evaluate a new approach to water quality control, provides a complete laboratory to test the feasibility and effectiveness of combining off-site nonpoint source treatment with traditional point source treatment to achieve water quality goals.

In the mid-1980s, the City of Boulder faced increased regulation of its wastewater treatment plant (WWTP) under state National Pollutant Discharge Elimination System permitting requirements, which protect the designated uses of receiving waters. One critical use was the warm water aquatic life below the wastewater discharge outlet in Boulder Creek. By evaluating data, city officials discovered that historic land use practices--agriculture, cattle grazing, surface mining, and water diversion-- accelerated and aggravated in-stream water quality problems and were degrading stream water quality and habitat. These practices included straightening and shortening the stream channel, creating a wider and shallower streambed, and losing riparian vegetation.

The Boulder Creek Enhancement Project's goal is to find out how best management practices can improve stream quality when used with traditional point source treatment at a publicly owned treatment works. The project investigates techniques to stabilize pH and temperature fluctuations and to reduce turbidity and un-ionized ammonia in the creek's main stem section. The project complements the city's conventional wastewater treatment plant.

In 1989 Boulder received a $75,000 grant under Colorado's Nonpoint Source Pollution Prevention Program to evaluate a new approach to water quality control, based on a 1987 feasibility study. Off-site stream improvements are also being evaluated to determine how NPS pollution limits the WWTP's effectiveness in controlling water quality at a critical point several miles below the plant's discharge. The initial project, completed in spring 1990, resulted in improving 1.3 stream miles. A second phase, completed in spring 1991, added 1.1 stream miles with an additional state grant for $75,000. With a section 319 grant of $42,000, another 0.5 miles was added the following spring. A fourth phase is being designed to improve an additional 1.7 miles using a mix of local and section 319 money. At its completion in 1994, the project will have improved 4.6 miles of channel below the WWTP.

BMPs that address each site's specific problems vary according to its current land use:

  • Cattle exclusion (fencing),
  • Bank stabilization,
  • Channel modification (thalweg pools),
  • Reaeration,
  • Wetland enhancement, and
  • Planting of riparian vegetation.

Dividing the project into phases allowed design improvements to be made on the initial BMPs, while Phase II and III BMPs were being built. Since the BMPs were all somewhat untried, this phasing was important to the project's success. It allowed improvements gained through early experience to improve later performance.

The Boulder Creek project has two goals. The first is to verify basic assumptions about how enhancing the riparian habitat affects the water quality. The second goal is to verify the cost, constructability, and durability of BMPs. Early attempts to construct a dynamic computer model of the Boulder Creek system showed that a full-scale demonstration project was the only practical means to test the effect of channel modifications, revegetation, and erosion control on in-stream quality and habitat.

Comprehensive testing allows sediment loads, hydraulics, weather, and other complex factors--such as algal growth within the stream--to occur in real time, rather than being simulated in a computer model. Projects such as Boulder Creek also require real-time verification since, unlike a computer model, seasonal and long-term effects cannot be quickly generated. Full-scale testing incorporates all the complex and synergistic effects that occur in a natural system and reflects a system more accurately than a model can.

The Boulder Creek project is transferable to other streams requiring similar treatment. Riparian restoration that can provide multiple benefits to wildlife, water quality, and property owners can increase the effectiveness of existing traditional treatment facilities.

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