The Frisco Sanitation District (District) owns and operates an advanced wastewater treatment (AWT) plant. Phosphorous removal has been the dominant concern at this wastewater treatment plant (WWTP) due to the potential for accelerated cultural eutrophication in Lake Dillon, which is a major recreational and drinking water supply in Summit County for the City of Denver.Peak flows are reaching the combined capacity of the four existing AWT units. Therefore, a pilot study was conducted to determine whether membrane filtration systems could (1) increase overall AWT throughput capacity, (2) meet phosphorous removal objectives, and (3) be cost competitive with conventional AWT treatment. Overall goals for the pilot study and preliminary design study include:Provide a net 1.0 mgd increase in AWT capacity.Achieve average effluent total phosphorus levels of <0.02 mg-P/L.Keep total construction cost, including membranes and all pumping, piping, and support facilities to less than $3,000,000.No increase in staffing requirements for either operations or maintenance (O&M).The pilot unit was a Zenon immersed membrane system. The pilot was operated for three months. Operational data included alum dose, long-term flux rate, backpulse and membrane cleaning frequency, and percent recovery. Permeate quality was tested for total phosphorous levels, turbidity removal, and the impact of pH on phosphorous removal performance.
The Phase 1 Source Water Quality Planning Study (Phase 1 Study) was completed for the City of Boulder (City) in April 2003. The purpose of the Phase 1 Study was to identify and recommend alternative approaches to improving and protecting source water for the Boulder Reservoir Water Treatment Facility (BRWTF). A large impetus for this study is the emerging regulations concerned with reducing the potential for occurrence of microbial pathogens, such as Cryptosporidium.The primary source of BRWTF raw water is Carter Lake. Raw water is delivered through a 21-mile open canal known as the Boulder Feeder Canal (BFC). The BFC discharges water either directly to the BRWTF or to Boulder Reservoir for later pumping to the BRWTF.The BFC generally follows a north to south route traversing the lower slopes of the foothills. As such, it tends to capture a significant amount of surface runoff that originates uphill and to the west. Although a riparian habitat along the canal could, to some extent, naturally attenuate contamination, the channel bottom and banks are regularly maintained to prevent growth of vegetation. Therefore, although the raw water at its source in Carter Lake is of a very high quality, significant degradation generally occurs as the water travels the length of the BFC.Boulder Reservoir is a shallow, Class 1 warm water reservoir with a surface area of approximately 700 acres and a storage capacity of about 13,270 acre-feet. It is used year-round for a variety of recreational activities, and therefore is subject to water quality degradation resulting from both body and non-body contact activities such as swimming and boating.During the summer, a natural temperature stratification occurs and a hypolimnetic layer low in dissolved oxygen forms at the bottom of the reservoir. This condition causes the uptake of soluble manganese from the reservoir sediment into the water and results in taste and odor treatment concerns at the BRWTF. In addition, the reservoir water is high in total dissolved solids (TDS), especially sodium, sulfate, and hardness. Wind action across the lake can increase the raw water turbidity up to 150 nephelometric turbidity units (ntu). Due to the shallow nature of the reservoir, algal blooms can occur throughout the year.The resulting variable water quality delivered to the BRWTF can pose significant treatment challenges to the City. The BRWTF staff must frequently adjust treatment operations in response to raw water quality changes from weather and human or animal activities. Operational changes in treatment are also required each time the raw water supply is switched between the BFC and Boulder Reservoir.Several source water management alternatives were explored as part of this study. These included:▪ Utilizing Boulder Reservoir as a year-round terminal reservoir. Management approaches associated with this alternative included:-Installing an aeration system to raise the dissolved oxygen concentration in the reservoir to above 5 milligram per liter.-Constructing bioretention facilities at all ...
The U.S. Environmental Protection Agency (USEPA) has relied on the small-scale prospective ground-water monitoring (SSGWM) study to evaluate the ground-water contamination potential of mobile and persistent pesticides for a number of years. Unlike in monolith lysimeter studies, mass balance of the applied pesticide cannot be determined in open field studies (such as the SSGWM study) without making assumptions about the distribution of residues in the subsurface environment. However, the recommended vadose zone pore-water and saturated zone ground-water sampling scheme in SSGWM studies may facilitate an approximation of mass balance of many pesticides with high leaching potential for an extended period. In one example, the mass of pesticide residues (including degradates) in ground water and the lower part of the vadose zone nearly two years after application represented the majority of the originally applied material. This high mass balance in a field study can be attributed to a combination of adequate sampling design and a high environmental persistence of pesticide residues. Open field studies like the SSGWM study and closed-system studies like the monolith lysimeter studies can be used together to provide a more complete picture of how leaching amounts relate to the level of ground-water contamination that may occur and how much mass of the pesticide is likely to leach under a variety of conditions. In the United States, regulations on pesticide use are designed to prevent ground-water pollution and to protect human health. The most recent legislation requiring regulation of the ground-water and surface-water impact of pesticide use is the Food Quality Protection Act of 1996. This Act requires that the Agency specifically determine concentrations of pesticides that may occur in drinking water as a part of dietary exposure assessments (7); the Agency must take action to ensure that pesticide dietary exposure will not occur at toxicologically significant levels. When a pesticide is determined to be a potential ground-water (or surface water) contaminant, USEPA must set health-based limits on residues in drinking water (regulatory limits are called Maximum Contaminant Levels, or MCLs) for that pesticide (2). These standards are based on the no-effect and low-effect levels determined in toxicity tests with mammals and therefore an MCL for a given pesticide could be much higher than 0.1 μg 1 -1 , the European Community standard for all pesticides.The SSGWM study is designed to provide information on the level of ground-water U.S. government work.
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