The greatest threat posed by reuse of wastewater is the potential for cross-connections between reuse and potable water systems. Of course, there are rules that prohibit cross-connections: rules 17-610 and 17-555 (now 62-610 and 62-555) Florida Administrative Codes (F.A.C.), and all the national plumbing codes prohibit cross-connections in plumbing systems. However, history shows that creating an environmental law or code does not necessarily ensure safety or compliance. This spring, there was a cross-connection between the reclaimed water system and a family's potable water plumbing in St. Petersburg; fortunately, no one became ill.(1) In Arizona, a cross-connection between the potable water system and a reclaimed water system at a private campground resulted in diarrheal illness in approximately 1,850 persons.(2) The United States Environmental Protection Agency reports that backflows were the cause of over 60,000 reported cases of illness from 1920-1980.(3) The potential for hazardous cross-connections can be expected to increase where reuse and potable systems are close together.
The best defense against liability from hazardous backflows is a good backflow prevention program. In fact, an acceptable program, prosecuted diligently and effectively, is the only legal defense according to a court precedent set in California.(4) Since 1976, the Florida Department of Environmental Regulation (FDER) has required community water systems to have a cross-connection control program although the agency has admitted enforcement is not always consistently diligent. Rule 62-610, F.A.C., requires applicants for reuse systems have their cross-connection control and inspection program approved by FDER. However, FDER's Drinking Water Section has no formal approval procedure. FDER indicated that the word `approved' will probably be changed to `acceptable' in future rule revisions. Meanwhile, FDER's Wastewater Section has provided assurances that permits are not issued for reclaimed systems until they are confident that the area served has an acceptable cross-connection control and inspection program. Program evaluation guidance is being developed and should be available to the districts soon.
Potential conflict or confusion may also occur between the permittee, usually the wastewater facility, and the distribution section which routinely manages the backflow prevention program. These conflicts can be magnified when these two systems have different owners.
UF/TREEO and the Florida Section of the American Water Works Association (FS/AWWA) conducted a backflow prevention survey in 1989 of utilities that serve 5,000 connections or more. Forty-three percent of the utilities responded. The majority of respondents (82%) described their utility as having an adequate backflow prevention program. However, 10% reported that no one is testing backflow preventers in their area, 32% indicated they did not have any type of surveying and retrofitting program, and 39% indicated they do not conduct on-site inspections prior to providing water service.(5)
What can a utility do to help prevent backflows from reclaimed water systems? Prevent cross-connections. According to rule 62-555.360(5)(b), F.A.C., cross-connection control programs with reuse systems "shall consider the following: (a) Enhanced public education efforts toward prevention of cross-connections. (b) Enhanced inspection programs, for portions of the distribution system in areas of reuse, for detection and elimination of cross connections." These should not be considerations; they are essential components of any "adequate" backflow prevention program. Surveys should not be restricted to areas of reuse; routine surveys are needed to protect the potable water distribution system and the customers served by it. In areas served by reuse water, make sure that the re-use water piping, valves and outlets are color coded, tagged, labeled or otherwise marked to differentiate them from other piping systems. This is required under rule 62-610.470, F.A.C. A variety of labeling/coding methods are being used: potable water PVC pipe marked "RE-USE WATER"; potable water PVC pipe marked with lavender marking tape, labeled "CAUTION-RECLAIM"; lavender PVC pipe, buried with yellow magnetic tape; brown PVC pipe. This variety demonstrates the potential for confusion between one system and the next. This is especially a problem in areas served by more than one utility.
Public education is critical because the public creates most cross-connections. Utilize bill stuffers. Speak at womens' clubs, business luncheons, and schools, or hold a seminar for the public. When the general public is being "sold" the merits of reclaimed water, make sure they also learn about the potential hazards of cross-connections. Currently, public education efforts vary significantly between utilities. Some reuse systems simply require customers to sign an agreement outlining their requirements and responsibilities. Another utility provides speakers to community service groups and schools; they also handout brochures and information packets to new reclaimed-water customers. One utility requires reclaimed water customers to attend a seminar that includes a tour of their virus lab. However, it is unclear how much information related to backflow prevention is provided as part of the public education process.
A few cross-connections will occur no matter how diligently we try to prevent them and, backflow preventers remain the best defense against backflow. FDER regulations currently allow air gaps; reduced pressure principle assemblies (RPs); double check valve assemblies (DCVA); pressure vacuum breakers (PVB); atmospheric vacuum breakers (AVB); and residential dual check valves. Dual checks, however, are only acceptable if the service has no other hazards requiring greater protection.
AWWA's M14 manual is the best source of guidance for matching the backflow preventer to the application or the hazard conditions at the site; rule 62-555.360(2) F.A.C., states programs should be developed using practices outlined in M14. The second edition of M14 recommends reduced pressure backflow preventer for premises served by reclaimed water systems. AWWA does not recognize the dual check as a backflow preventer.(2) This recommendation appears to be in conflict with Florida regulations that allow a residential dual check. However, state regulations do allow local codes, ordinances, or regulations to require a higher level of protection.
Just what is the hazard level of reclaimed water? Frequently we hear that reclaimed water is "just about as pure as drinking water". There are different treatment levels for reclaimed water depending upon the intended use. Table 1 outlines the general treatment requirements based on the intended use for reclaimed-water most liable to be cross-connected to potable water systems. Reclaimed water systems supplying residential lawn irrigation systems, edible crops, toilets (in commercial or industrial facilities), fire protection systems, etc., are probably most susceptible to cross-connections. For this reason, this type of reclaimed water receives a fairly high degree of treatment: secondary treatment, high-level disinfection, and filtration. High level disinfection means that 75% of the daily monitoring samples are required to be free of fecal coliforms; the remaining 25% are required to contain no more than 25 fecal coliforms per 100 ml sample. By comparison, community drinking water must have no more than one positive total coliform sample per month if the system serves <33,000 clients, and less than 5% positive total coliform samples per month if the system serves >33,000 clients; detection of coliforms beyond these limits poses a "non-acute health risk" and repeat samples must be taken. Any fecal coliform-positive, E. coli-positive, or total coliform-positive repeat sample is considered a violation that poses an "acute risk to health".
Clearly, even reclaimed water that receives high level disinfection could often pose an acute health risk if drinking water standards were applied. This doesn't even take into consideration the long list of chemical contaminants tested for in potable water systems. It should be noted that several cities are conducting additional tests on their reclaimed water. Items being monitored include: heavy metals, nitrogen, pathogens, viruses, priority pollutants, phosphous, and volatile organics. An analysis of these test results would help in clarifying the risks associated with reclaimed-water. This analysis could also provide valuable information about the level of substances commonly found in reuse water. The potable water distribution system could then be routinely monitered for substances, e.g., phosphorus, that `indicate' a cross-connection between the reuse and potable water systems.
In a potable water distribution system, monitoring is done at representative points. However, for reuse water, the regulations require monitoring samples be taken prior to discharge to holding ponds or the reuse system. Since the regulations do not require maintenance of a chlorine residual within the reclaimed water distribution system, regrowth of microorganisms seems certain. In addition, because reclaimed water is often stored in golf course lakes, lagoons, ponds, or uncovered tanks, the potential for post-treatment contamination exists. The amount of disinfectant maintained in potable water distribution systems is provided mainly to prevent regrowth and is frequently not sufficient to effectively deal with contaminants added through cross-connections. Those systems utilizing chloramines face an even bigger problem, since at least one study has shown that chloramines are relatively inefficient at protecting against contaminates introduced after the treatment process and chloramines fail to act as an indicator of contamination.(6) A "total chlorine residual is present even after the addition of sizeable amounts of contaminatory materials", thus "the detection of a combined chlorine residual does not assure water potability".(6)
Is reclaimed water a health hazard or a non-health hazard? AWWA feels it is a health hazard and recommends the use of a reduced pressure principle assembly.(2) California has also taken the position that it presents a health hazard; the wastewater treatment level for irrigation of public access areas in California is similar to Florida (Table 1).(7) & (8)
What is the difference between a dual check valve and a double check valve assembly? Double check valve assemblies that are "approved" by the Foundation for Cross-Connection Control and Hydraulic Research at the University of Southern California (the Foundation) must be testable and repairable in-line. Approved double check assemblies also must have resilient-seated, full-flow characteristic shut-off valves on each end of the assembly, as well as four test cocks. Dual checks, on the other hand, are not normally supplied with valves or test cocks. Most are repairable, but many must be removed from service in order to be repaired or tested. For approval, double check valve assemblies must meet rigorous specifications and pass extensive tests including a one-year field evaluation. By contrast, dual check valves are not field tested and are not subjected to the same rigorous testing required of approved backflow preventers. Proponents of reuse systems frequently point out that there is a big difference in the initial cost of dual checks and double checks. A basic three-quarter inch dual check usually costs approximately $15.00, while an equivalent approved double check valve assembly costs around $50.00. Some manufacturers market dual checks that can be tested and serviced in-line. However, the costs increase significantly when test cocks and shut-off valves are added to these devices. Some resetters are designed to make servicing dual checks more convenient, but again, this increases the cost of the installation. A resetter and a dual check valve can cost as much as $40.00.
Maintenance and repair costs must also be taken into consideration. Approved backflow prevention assemblies should be tested at least annually, as outlined by AWWA M14, the Foundation, and all manufacturers' literature. It seems logical that dual checks should receive more frequent testing, since they do not have to meet the same rigorous approval requirements. In a TREEO telephone survey, several utilities were asked how often they test or repair dual checks. A number of them indicated that there were no plans to test or replace these valves. Only one utility indicated they plan to test them annually. Most utilities responded that they plan to replace the valve when water meters are changed. Their regular water meter change-out programs will result in dual check valve change frequencies ranging from 4 to 15 years. The annual failure rates of approved assemblies varies from 10% to 40% and manufacturers of these valves recommend testing at least every two years. Based on the failure rates of approved assemblies, it should be assumed that both check valves in most dual check valves will fail sometime before 5 years.
Of course, the big problem utilities face is how to possibly test and service all these valves annually? How many extra employees will they have to hire? Or how much will they have to pay a private contractor? Another viable option is to make the customer responsible for hiring a properly trained individual to service the valve.
Just installing these devices and never testing or replacing them gives the public and the purveyor a false sense of security. Under these circumstances, it is questionable whether dual checks really are "better than nothing", as is commonly stated.
The potential for cross-connections and backflows will increase as reclaimed water lines are installed near potable water lines. The best defense against backflows is a well developed backflow prevention program. Preventing cross-connections, via plan and site review of new construction, and surveying and retrofitting of existing facilities, should be a major focus of that program. Selection of the appropriate backflow preventer should also be made with care; the decision made should be defendable in court. This is also true for the maintenance and repair program. While reclaimed water does receive a fairly high degree of treatment, it is important to bear in mind, post-treatment contamination and regrowth can affect the quality of the water once it leaves the wastewater treatment plant.
Reclaiming wastewater is a great idea; however, there are risks associated with its use. These risks increase significantly if we fail to recognize and acknowledge them. Wastewater reclamation programs should "assure health protection without unnecessarily discouraging wastewater reclamation".(8) Definitely this valuable resource should be utilized, however, the emphasis should be placed on doing so in a safe manner.
|TYPE OF USE||COLIFORM LIMITS||TREATMENT LEVEL|
PUBLIC ACCESS AREAS,
ALSO: golf courses, cemeteries, parks, fire protection, toilet flushing
|75 % of the samples:
no fecal coliforms
25 % of the samples:
High Level Disinfection
≤ 5 mg/L TSS
RESTRICTED PUBLIC ACCESS
≤ 200 fecal coliforms per 100 ml.
≤ 10% of the samples can exceed 400 fecal coliforms
No one sample can exceed 800 fecal coliforms
≤ 10 mg/L TSS
OVERLAND FLOW SYSTEMS:
Uses: Applied to upper reaches of terrace sloped vegetated surfaces e.g., sod farms, forests, fodder crops, pasture lands
|≤ 2400 fecal coliforms per 100 ml.||
< Secondary Treatment:
BOD: 40-60 mg/L
TSS: 40-60 mg/L
|Spray irrigation of food crops
Landscape irrigation (parks, playgrounds)
Non-restricted recreational impoundments
≤ 2.2 total coliforms per 100 ml.
≤ 23 total coliforms per 100 ml.
oxidation, coagulation, clarification, filtration, & disinfection
≤ 2 ntu average 5% samples:
Robin L. Ritland is a training specialist at the UF/TREEO Center and the author of Backflow Prevention: Theory & Practice.
Les O'Brien a Senior Training Specialist at the UF/TREEO Center, has been instructing courses in backflow prevention at TREEO for over eight years; he is the immediate past-president of the American Backflow Prevention Assoc (ABPA).