All the water that ever was or will be on earth is here right now. More than 97% of the Earth’s water is within the in oceans. The remaining 2.8% is the water within the land masses, as groundwater, rivers, streams, lakes, and within the ice caps and glaciers (over 77% of fresh water is currently frozen). Only a fraction of water falls as rain each year to make the rivers flow, recharge lakes and groundwater. The water on earth never rests, it is constantly moving within the hydrologic cycle along various complex pathways and over a wide variety of time scales. Water moves quickly through some pathways -rain falling in summer may return to the atmosphere in a matter of hours or days by evaporation. Water may travel through other pathways for years, decades, centuries, or more. As the demand for water grows in our population centers, we are straining to meet the demand. Even in generally water rich areas there are limits to the availability of water and United States has slowly and quietly begun to address the availability of water by recycling the water.
Direct water recycling is reusing treated wastewater for beneficial purposes such as agricultural and landscape irrigation, industrial processes, toilet flushing, and replenishing a ground water basin (referred to as ground water recharge) and less commonly returning the water directly to reservoirs. Since 1978, the upper Occoquan Sewage Authority has been discharging recycled water into a stream above Occoquan Reservoir, one of the two potable water supply sources for Fairfax County, Virginia. Recycled water has been part of the Occoquan supply for 34 years and chances are if you are in Fairfax, parts of Prince William and Loudoun counties you have been regularly drinking recycled water. Noman M. Cole, Jr., a very forward thinking engineer, developed the Occoquan Watershed Policy in 1971. This policy was the acknowledgment that to continue supplying the region with drinking water, the Occoquan Reservoir would be used both for wastewater disposal and public water supply. To do this and protect public health the Occoquan Watershed Policy not only specified the type of waste treatment practices that would have to be adopted on a basin-wide scale, but it provided for an on-going program of water quality monitoring to measure the success (or failure) of the waste water treatment. This resulted in the construction of the Upper Occoquan Service Authority, UOSA, advanced wastewater treatment plant with tertiary treatment to replace the eleven small secondary treatment plants.
Wastewater treatment within the basin would have three stages of treatment, primary, secondary and tertiary or advanced treatment. Primary Treatment consists of sedimentation and screening of large debris using screens and large settling tanks. Until 1960’s primary treatment was the only form of sewage treatment in most places. Secondary treatments usually include biological and/or chemical treatment. One of the most common biological treatments is the activated sludge process; in which primary wastewater is mixed with bacteria that break down organic matter and cleans the water. Oxygen is pumped into the mixture. A clarifying tank allows sludge to settle to the bottom and then the treated wastewater moves on for tertiary treatment. Coagulation, filtration and disinfection take place in tertiary treatment. A coagulant is added, UOSA uses the high-lime process to reduce phosphorus to below 0.10 mg/L. This process also serves as a barrier to viruses, captures organics leaving secondary treatment, and precipitates heavy metals and other suspended particles. The UOSA permit requires total suspended solids, TSS, below 1 mg/L and chemical oxygen demand, COD, below 10 mg/L. To meet these stringent levels, multimedia filtration and activated carbon are used. Filtration removes organic matter, microorganisms and mineral compounds, and excess nutrients. The final barrier to pathogens is a chlorination and dechlorination process. UOSA uses sodium hypochlorite and sodium bisulfite. UOSA is has an expansion program underway to expand capacity to 54 million gallons a day, but according to 2012 Fairfax County disclosures, the plant currently operates closer to an average of just over 13 million gallons a day.
After disinfection the reclaimed water is released to the watershed cleaner than the rest of the river, according to Dr. Tom Gizzard ofthe Occoquan Watershed Laboratory. Financed by the wastewater treatment plants and Fairfax Water, the Occoquan Watershed Laboratory (OWL), was established by the Virginia Polytechnic Institute Department of Civil Engineering. The laboratory began its Fairfax operations in 1972, and has conducted comprehensive studies of receiving water quality, and effects of the waste water treatment effluents for 40 years. The current Director of the Laboratory is Dr. Tom Grizzard, professor of Civil Engineering at Virginia Polytechnic Institute and State University (Virginia Tech). When I spoke to Dr. Grizzard he pointed out that the water released into the Occoquan is “highly reclaimed wastewater” and not sewage effluent. There is a difference and Dr. Grizzard and the OWL staff make sure of it.
The Occoquan Watershed Policy is the oldest and largest reservoir augmentation program in the county and the second largest water recycling program in the country. The largest water recycling or reclamation program in the country and in the world belongs to the Orange County Water District and the Orange County Sanitation District jointly owned and developed the Groundwater Replenishment (GWR) system, the world’s largest water purification plant for groundwater recharge. The GWR System diverts secondary treated sewer water and purifies it through a series of tertiary treatments: microfiltration, reverse osmosis, ultraviolet disinfection and hydrogen peroxide. The cleaned water is returned to the groundwater basin to increase both the water supply and quality rather than discharging the treated sewer water to the ocean. The additional treatment of the wastewater is much cheaper that desalinization and makes the groundwater use sustainable-utilizing the groundwater basin as a reservoir.
In Fairfax County Virginia, water is withdrawn from the Potomac River and the Occoquan Reservoir and filtered, cleaned, disinfected and delivered as drinking water to the homes and businesses throughout the county (and in parts of Prince William and Loudoun Counties). Waste water from toilets, sinks, drains is collected by the sewer systems and six waste watertreatment plants that serve some portion of Fairfax County. On average, Fairfax County uses 160 million gallons of drinking water per day from both the Corbalis plant and the Griffith plant drinking water plants. The combined total capacity of both plants is 345 million gallons/day. The drinking water systems are sized to deliver the peak demand on a 100 degree day when everyone is doing laundry and watering their lawns and everything else we do with water on hot summer days. Most of that water (except what is used to irrigate landscaping) finds its way to a waste water treatment plant within the region. The wastewater processed in Fairfax County is fully treated and released into the river and streams of the Potomac watershed. (We will ignore the issues currently being addressed at Blue Plains.) To ensure the continuation of water supply during droughts, Fairfax is party to a low flow allocation agreement with the members of the Interstate Commission on the Potomac River Basin, ICPRB. In addition, Fairfax bought the rights to 14 billion gallons of water from the Jennings Randolph Reservoir. On an ongoing basis ICPRB coordinates Fairfax Water’s low flow water withdrawals between the Potomac and Occoquan. The Occoquan Reservoir contains 11 billion gallons that receives both natural river flow and about 13 million gallons of reclaimed water daily.
|From Fairfax County|
Noman M. Cole, Jr. Pollution Control Plant (named in honor of the engineer) is now engaged in a direct water recycling program, reusing treated wastewater for landscape irrigation and industrial processes. The Noman Cole plant releases its reclaimed water to Pohick Creek. Now the plant is engaged in the Water Reuse Project also known as the Purple Pipe Project, to directly reuse some of the water. (The pipes are colored purple to designate the water as non-potable.) The Purple Pipe project has completed the first phase of the project and is delivering 1.4-1.6 million gallons of fully treated waste water to the Covanta Fairfax, Inc. Resource Recovery Plant and Laurel Hill Golf Course via a recently constructed 5 mile purple pipeline, two large pumps, instrumentation and hypochloride disinfection. The Laurel Hill Golf Course will use the water to augment the on-site irrigation lake during the summer. Due to recent rains, the demand for water by the golf club is limited, but according to Michael McGrath the Director, Wastewater Treatment Division, Department of Public Works and Environmental Services, for Fairfax County, the Laurel Hills Golf Club can draw up to 27 million gallons a year of reclaimed water from the Noman Cole Plant. The Covanta Resource Recovery Plant is allowed to use up to 560 million gallons a year of Purple Pipe Water to irrigate the adjacent athletic fields and other purposes. The Noman Cole plant discharges and average of 45 million gallons a day to Pohick Creek, so this is just a small fraction of the daily flow. The reclaimed water from Noman Cole makes up a significant flow to Pohick Creek so that there is a minimum environmental flow that should continue, but there is opportunity for growth in the Purple Pipe Project.
The project, which began in 2009, cost $16 million for the first phase (or about $600 per foot) with $6.5 million in funding coming from the federal stimulus funds through the American Recovery and Reinvestment Act, and the remainder was paid for by Fairfax county through a loan from the Virginia Department of Environmental Quality Clean Water Revolving Fund Loan Program. In the first partial year of operation the project will produce about 20,000 credits for Noman Cole Plant in the Virginia Nutrient Trading Program in addition to the reduced cost water. Nutrient trading programs provide wastewater treatment plants with flexible options for meeting and maintaining permitted nutrient load limits, but also could be used to meet the approximately 25% reduction in nutrients required under the federally mandated Chesapeake Bay TMDL. A nutrient credit is a reduction of one pound of nitrogen and worth (at the current time) $2. Though the first phase of the Purple Pipe Project will generate more credits next year, still at $2 per credit plus the price received for water and costs or $600 per foot there is virtually no way for Fairfax to utilize Purple Pipe to meet the TMDL goals or increase water supply without a significant rate increases for water and large volume users. If using reclaimed water is necessary for the region to maintain its quality of life, the cost of water will have to rise to cover the costs because we are already using all the cheap water.
The numbers break down like this: this project would have to produce cash flow of about $918,000 per year (rather than the projected under $200,000 for water and nutrient credits) to pay for the $16,000,000 cost at 3% interest (current AAA interest for 20 year bonds is above 3%) over 25 years. (Though for this project the $6.5 million from the federal stimulus funds does not have to be repaid.) The Purple Pipe project is a very cool project, but at the current cost of water the capital costs are prohibitive. Or maybe, we've just had a glimpse of the marginal cost of water.