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By Amy Sorkin Kurland
Most of us in the United States take indoor plumbing for granted. But there is actually a small percentage of Americans who see this otherwise-considered necessity as a luxury. A number of such residents can be found in the Dawn Community of Caroline County, VA. However, a recent and ongoing renovation project called the Dawn Wastewater and Housing Rehabilitation Project (DWHRP) has been cleaning up the subpar situation of malfunctioning septic tanks and drainfields at 153 residences in the area.
Before the DWHRP began, 19 of the homes in what is referred to as the Dawn service area—a collection of residences that stretches over a 55,000-acre area—were actually functioning with no indoor plumbing whatsoever. They had been using portable toilets or pit privies.
Others homes had failed or marginally functioning septic systems. In short, the area was a mess and a threat to the health and welfare of those who lived there. The situation was so severe that the Dawn service area was cited by the environmental health supervisor of the Rappahannock Area Health District as “the worst area I have seen for onsite sewage disposal systems.”
The reason the area had progressed to such a point was not because of negligence on the part of the county government, which had been trying to come up with a solution for at least 8 or 9 years, but rather because the county could not afford the capital and operational costs that came with conventional solutions. There were two main reasons for this. First, the Dawn service area is very rural, so the homes are very spread out. “When you design and finance a system, it’s paid for by the number of customers on the system,” explains John Warwick, lead engineer on the DWHRP and project engineer with Arcadis G&M. Inc., an engineering firm based in Denver, CO, with branch offices throughout the United States, including Richmond, VA. “The more customers you have per mile of pipe, generally the more financially feasible the project is. But if you have only a few customers per mile of pipe, the cost in proportion to the number of customers goes way up.”
Secondly, the Dawn service area is made up of many lower- to middle-income homes, which put additional strains on the budget for this project because the county did not want the service charge per home to exceed $25 a month.
Engineers To The Rescue
In 2004, Caroline County hired Arcadis G&M Inc. to come up with a solution that the county and residents could afford. All the homes in the Dawn community service area use wells for their water supply, and many of the wells were contaminated due to the non-functioning septic systems. Since there was not a centralized sewage system anywhere near the Dawn Community, hooking the area up to that was not a financially feasible option. So the big challenge was coming up with a decentralized system whose operational and maintenance costs remained within the $25-a-month-per-home budget.
“If you look to the conventional type of package plants, those were just too expensive,” says Warwick. “And we didn’t want to force everyone to hook up to this system, we only wanted it to serve those who requested it.”
Phase 1 of the DWHRP was designed to provide 150-plus homes with a well-functioning community sewer system that would allow for expansion as needed in the future. “Essentially we looked at the most cost-effective ways of solving the problem for three particular categories: collection, treatment, and disposal. We evaluated the alternatives in each category and came up with the best for this particular project, using as a base the combination of capital costs and operation costs.”
Low Pressure, High Savings
A low-pressure sewer system was ultimately selected for collection. The alternatives considered were a gravity system, a vacuum system, and a pressure sewer system. The low-pressure system was selected largely because it had the lowest capital and operational cost compared to the other systems. The system chosen was installed using a series of small, plastic pipes that convey water the way a garden hose does. “This is the most cost-effective way of conveying the liquid portion of the sewage to the treatment facility,” explains Warwick. “The pipes come in 500-foot-long rolls, much like a large coil of wire. We’re using a directional boring machine to put the pipes 3–4 feet below the ground surface 500 feet at a time. We don’t have to dig up any roads, and no one even sees the system being installed as it runs by their house. It’s also significantly less expensive than the conventional methods of construction using backhoes and open trenches.” The low-pressure system really helped lower the cost of construction, and installation is also very quick. Other advantages include the fact that the wastewater can be carried uphill and that the system is very strong because it has joints every 500 feet only.
Taming The Waste
The treatment system selected for Dawn Community is centered around a Bio-Microbics product called the FAST (Fixed Film Activated Sludge Treatment) system. The treatment plant site, which is about 1,000 feet from the closest home, consists of six FAST units. “The FAST process is a fixed-film, aerated system utilizing a combination of attached and suspended growth, capable of nitrification and denitrification in a single tank. It combines the stability of a fixed-film media and the effectiveness of proven, activated sludge treatment, making it very reliable,” says Warwick.
One of the advantages of this system is the ease of installation. Hardly any labor is required to be done in the field, since the tank the FAST unit is installed into is precast. “You simply dig a hole to put in the precast concrete tank, lower the tank into the hole, backfill around it, then bring in the FAST unit, bolt it in place, and put the concrete top on it. You could actually build this plant with two people,” says Warwick.
“In the planning process of this project, we thought there were going to be only 150 homes served, but since construction is over 50% complete we’ve had 20 more sign up for service, and another list of 20 on top of that are currently in the process of completing applications for service. It will likely total around 200 homes by the time the construction is complete, and we won’t even have to add another FAST unit.” But if they did need to, it’s nice to know they could install another one in just a few days.
Dealing With The Solids
FAST units are great for treating the liquids. But first the issue of separating the solids must be dealt with. “On these small, decentralized systems, it’s not usually cost-effective to build and construct a separate solids handling facility if the county already has a major significant treatment plant. This is the case in Caroline County,” says Warwick. Caroline County’s treatment plant already had plenty of capacity for solids. So what Arcadis did was put in a system that looks just like a septic tank at each home. These are called STEP tanks. Their sole purpose is to separate the solids from the liquids, store the solids, then pump the liquids to the remote treatment site.
Arcadis chose to have a septic tank pump truck come to the homes periodically to remove the solid portion of the wastes from the tank and haul them to the treatment plant for further treatment and disposal. “We chose to do this solids separation step at each home instead of at the treatment facility because we didn’t want the solids to be in the collection lines. Also, a truck can only carry so much. Not having solids in the lines also cuts down tremendously on maintenance costs.”
Liquid Solutions
Once the liquid wastewater reaches the main treatment-plant site, where six FAST units are located, it’s biologically treated using zero chemicals. The biological process of the FAST units is very similar to other biological systems, but Bio-Microbics has simplified the process and put a supercharger on it to get the same amount of treatment in a much smaller space. “It provides a very high degree of treatment in a small space. What they’ve done is wrap it all in a very low-maintenance-type package that works very well,” adds Warwick.
Besides providing high-quality treatment in a smaller space, the FAST system had several other advantages that made it very attractive for the Dawn service area. First, it was the most economical system Arcadis evaluated based on capital and installation costs. Second, it had the lowest operation and maintenance costs compared to all the other systems that were evaluated for this project. Another major benefit is that the only thing the system requires to make it run is one blower motor, which simplifies maintenance. “It’s like a light switch in that it’s either on or off,” says Warwick. “If there’s something wrong we know it because it won’t work at all. These systems are simple, reliable, easy to operate, and cost-effective. They’re also easy to construct.”
One of the best things about using the FAST units is that because they are modular, they’re more economical to operate. That’s because if the amount of flow does not require all units to run, the ones that aren’t needed can stay off. Consequently, one or more can be taken offline if not needed, and if a unit or a blower does go down, the rest of the system can easily handle it.
Where Does It All Go From Here?
For disposal, Arcadis chose the process known as low-pressure dosing. At the treatment and disposal site, the good soils were 30-40 inches below the ground surface, so underground disposal was the smart choice here. The site did, however, provide a challenge: For about 50 years it has been used to grow pine trees, and the county wanted to minimize disturbance of the logging operation there as much as possible. So when a low-pressure-dosing system was installed, special considerations were made to minimize the disturbance to the forested area. For instance, the county will replant pine trees in and around the disposal-site area when the project is completed. “This will aid in further nitrogen uptake,” says Warwick, “which will provide additional treatment as well as help the trees to grow faster.”
The low-pressure-dosing system selected is like a septic-tank drainfield but pressurized. It’s a shallow, pressure-dosed soil-absorption system that contains a network of small-diameter, perforated pipes placed 36-42 inches deep into 6-foot-wide trenches.
“We probably could have used gravity lines here, but we wanted to get the liquid into the ground quickly, and to do that we needed pressure.” Again, the low capital cost for construction and ease of operation were two big motivators for choosing a low-pressure dosing system. Among other advantages are that less land area is required for the absorption system compared with a gravity-flow drainfield, pressurized distribution disperses the effluent more uniformly through the drainfield, and the placement of the trenches promotes growth of aerobic bacteria.
The Learning Point
The individual STEP tanks located at each house require power. Their function is to separate the solids and pump the liquid portion of the wastewater to the central treatment facility. Although it’s only a small motor that powers the pump inside this tank, a new circuit needs to be run from an electrical panel in the house to a junction box on the side of the house. Although this may sound like a relatively simple task, the electrical facilities available in many of the residences in the Dawn community made this objective quite a challenge. “What we came across was that many of the homes didn’t have big enough panels and did not have the extra capacity to provide the additional service to the STEP tanks,” explains Warwick.
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| Advanced control units, STEP tanks, and FAST units add up to a cost-effective system for decentralized wastewater treatment.
It is hoped that these features will make the Dawn Community in Caroline County, VA, a showcase inspiring similar
projects throughout the United States. |
Not wanting to replace a bunch of panels to get the system up and running, Arcadis did more research and collaborated with the local power company. “We came up with a device that goes behind the electric meter on the outside of the house. It provides a circuit so you can run a wire on the outside of the house to a disconnect switch without having to go in the house.” This process proved to be not only effective, but a very inexpensive solution as well.
With the exception of that obstacle, all in all the project has been going very smoothly. Warwick believes that one of the reasons for this is that Arcadis and the county made a concerted effort to communicate and reach out to all parties that would be affected by this project. This ran the gamut from county officials and funding-agency representatives to several prominent members of the Dawn Community who represented the residents. In addition, the help of specialists in public relations and funding administration expedited the communication process while optimizing efficiency. By educating all parties involved about the technologies available, and by inviting them to give input and feedback on the solutions presented, Arcadis and the county were able to create trust and community support, providing a project that gave the maximum benefit for the minimum cost. All of this made it a lot easier to secure the funding needed for the project’s construction.
How It All Fell Into Place
Installation began in February 2006. The goal of Phase 1 is to serve the initial 153 homes plus others that signed up for service during the construction period. The plan is that the first half of the system will be up and running early in 2007.
The installation process for the STEP tank at each house does affect the residents, but only minimally as they can continue using their old system while the new one is being installed. The majority of the 153 houses have an existing septic tank that needs to be abandoned (old, leaking, full, etc.). In these cases, installation includes putting a new tank next to the old one, usually about 10 feet away, and then digging a hole and setting the new tank in it. Once the tank is set, it’s backfilled with soil and seeded.
As far as maintenance is concerned, the Dawn wastewater treatment system will be monitored by a remote monitoring device. This allows the county to look at how much flow is going through the treatment system, how many times the dosing pumps come on each day, how long they run, which blowers are running, power outages, and what the liquid level is in each of the tanks.
The system has an alarm, and if it goes off it will begin dialing the telephone numbers of key people in charge of the facility to let them know something at the plant needs attention. “This is a very inexpensive system to put in, and you don’t have to have telephone lines—nothing but 110-volt power. It also has its own battery backup to continue the monitoring process even if all power to the facility is lost. This method is very cost-effective because you don’t need an operator stationed at the plant.”
A number of manufacturers make these monitoring systems, and the one used at the Dawn treatment site is one of the smaller ones out there. It costs in the neighborhood of about $3,000. To operate it, the monthly expense incurred is a satellite phone fee, which runs roughly about $30 per month on average. The main thing Warwick wants to emphasize is that by using the latest technology available—not necessarily the conventional technology—operation costs can be lowered.
Why aren’t more people using this technology?
The total construction cost of Phase 1 of the project was $3,279,000. “In most large cities, people are paying $40 a month or more for this service,” says Warwick. “So this is really a neat project and we’re hoping it becomes a showcase for other areas in need of a cost-effective solution throughout the country.”
If these less conventional and newer technologies are just as effective—and often more effective—than conventional systems, and they also cost less, why are so many people sticking with the traditional sewage collection, treatment, and disposal technologies? Warwick believes it’s largely because most people don’t take the time necessary to really research all the options available in the market today. It’s easier to do what someone before you has already done, but it takes a lot more effort to try to come up with a new, more cost-effective way of doing something.
The FAST units, although less expensive than comparable conventional systems, have actually been on the market for quite some time. “One of the challenges is simply convincing people that decentralized wastewater treatment and disposal is a technically sound and long-term solution that is more affordable and can be managed safely.” Since part of the training for engineers and utility operators is the operation of larger centralized systems, the popular mindset tends to be that these are simply what is always best to use. “There’s a feeling in the country that decentralized wastewater treatment is just a Band-Aid until central sewers arrive. And that’s the mindset we have to correct,” says Warwick.
And he’s hoping that the DWHRP will begin the process of opening people’s eyes and minds to the possibilities of decentralized wastewater treatment as a permanent, efficient, and cost-effective solution. With centralized sewage systems, the water is discharged into an all-season stream, which means it’s lost to the environment. With decentralized wastewater treatment systems that dispose of the treated effluent in the ground, it goes back and is recycled to recharge the groundwater aquifer and be reused.
“There are scores if not hundreds of communities in Virginia that are in the same situation as the Dawn Community in Caroline County was,” concludes Warwick. “What this project will show is that decentralized sewer systems are an economically and environmentally responsible choice—and that they’re also an intelligent and effective alternative to big-pipe sewers.”
Journalist Amy Sorkin Kurland specializes in marketing communications
OW - January/February 2007 |
