Environews Spheres of Influence

When combined sewer systems wereintroduced in 1855, they were

hailed as a vast improvement over urbancesspool ditches that ran along city streetsand spilled over when it rained. These net-works of underground pipes were designedto dry out streets by collecting rainwaterrunoff, domestic sewage from newlyinvented flush toilets, and industrial waste-water all in the same pipe. Waste- andstormwater was then discharged directlyinto waterways; in the early twentieth cen-tury, sewage treatment plants were addedto clean the wastewater before it hitstreams. Combined sewer systems were—and still are—a great idea, with one catch:when too much stormwater is added to theflow of raw sewage, the result is frequentlyan overflow. These combined sewer over-flows (CSOs) have become the focus of a

debate regarding the best techniques tomanage growing volumes of sewage andstormwater runoff in many older U.S.communities.

In dry weather, a combined sewer sys-tem sends a town’s entire volume of waste-water to a sewage plant, which treats anddischarges it into a waterway. Rain andsnowmelt, however, can fill up a combinedsewer. The sewers have been specificallydesigned with escape overflow pipes so thatthe mixture of sewage and stormwaterdoesn’t back up into buildings, includinghomes. The resulting CSO dumps rawsewage into lakes, rivers, and coastalwaters, potentially harming public healthand the environment.

In April 1994, the U.S. EnvironmentalProtection Agency (EPA) issued the CSOControl Policy, the national framework for

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control of CSOs, through the NationalPollutant Discharge Elimination Systempermitting program. This policy mandatedthat communities dramatically reduce oreliminate their CSOs, and the agencybegan working with municipalities toimprove antiquated sewage systems so theycould reach Clean Water Act goals. Underthis policy, communities with combinedsewer systems must establish a short-termplan to control these discharges as well as along-term control plan.

The EPA’s mandate on CSOs leavescommunities with two basic options,according to Joan B. Rose, a public healthmicrobiologist at Michigan State Uni-versity. Communities with CSOs can buildseparate underground pipes forsewage and stormwater. Or they cankeep their combined pipes and some-how build more capacity. “But if theyshut down [combined sewer sys-tems],” she says, “communities mustfind a way to store or treat peak flowswhen it rains.”

When CSOs OccurAbout 40 million people in 32 stateslive in cities with combined sewer sys-tems; most of these systems are foundin Maine, New York, Pennsylvania,West Virginia, Ohio, Indiana,Michigan, and Illinois. CSOs are amajor water pollution concern for772 cities, according to the EPA’s2004 Report to Congress: Impacts andControl of CSOs and SSOs [sanitarysewer overflows, which are associatedwith another type of sewer system].

Although some major cities likeNew York City and Philadelphia havecombined sewer systems, most com-munities with CSO problems havefewer than 10,000 people, accordingto the EPA report. One reason lies inthe economy of scale: larger munici-palities are more likely to have suffi-cient tax base and water users tofinance remedies to CSO problems.

CSOs annually result in an esti-mated 850 billion gallons of untreat-ed wastewater and stormwater being dis-charged into U.S. waterways, according tothe EPA report. Thanks to the CSOControl Policy, this is an improvementover figures in the agency’s 2001 reporton the same topic, which put the figure at1.3 trillion gallons per year.

CSOs flood waterways with contami-nants including microbial pathogens, sus-pended solids, chemicals, trash, andnutrients that deplete dissolved oxygen.Microbial pathogens and toxics can be pre-sent in CSOs at levels that pose risks to

human health. CSOs can therefore lead tocontamination of drinking water supplies,beaches, and shellfish beds.

The EPA’s 2004 report indicated thatthe agency has limited information on theextent of human health impacts of CSOs.One health effect the agency can quantifycomes from regularly monitored coastaland Great Lakes beaches. Using data fromthese locations, the EPA estimates about3,500–5,500 gastrointestinal illnesses eachyear are caused by CSO and SSO pollutionof swimming waters.

According to Rose, current estimateshold that microbial pathogens in U.S.public drinking water supplies sicken hun-dreds of thousands of people each year,

though most of these waterborne illnessesare mild, disappearing after a few days. It’sdifficult, moreover, to trace sources ofthese illnesses. Many outbreaks in theUnited States go unreported, and in mostoutbreaks the pathogen is not identified.CSOs may or may not be to blame.

However, several reports and studies,including one from the 22 November2002 Morbidity and Mortality WeeklyReport, demonstrate that there has been anincrease in waterborne disease outbreaks inthe United States over the past few years.

Rose says these community outbreaks arecorrelated with rainfall as well as associatedoverflows and leaks in public sewer sys-tems. Sensitive populations—the elderly,the very young, and those with existinghealth problems—are most vulnerable towaterborne enteric microorganisms. Thesepopulations make up about 20% of theU.S. public.

A Controversial AlternativeIn most municipal treatment plants, waste-water usually goes through a two-stepprocess before it is discharged into lakes,rivers, and coastal waters. Large solids areremoved first during primary treatment—mechanical screens remove large debris,

and sedimentation tanks removesludge (solids that sink) and scum(elements that rise to the top). In thesecond step, wastewater is first routedto tanks with activated microbes thatbreak down organic materials andremove some pathogens and more ofthe remaining solids. This biologicaltreatment can improve the effective-ness of disinfection, which is often thesecond part of this step—chlorine isused to kill bacteria and other remain-ing pathogens before the water isreleased.

This treatment process is the mosteffective way to ensure that effluent isclean. It has become the required stan-dard for wastewater treatment underthe Clean Water Act. But many plantshave smaller biological treatmentcapacities than primary treatmentcapacities. Biological treatment facili-ties are expensive, and many commu-nities have outgrown systems that werebuilt 30–40 years ago. Moreover, thesefacilities can be delicate. Large waste-water flows into biological treatmentunits, such as those following heavyrains, can wash the microorganismsfrom the tanks. The units must thenbe shut down until the microbial pop-ulation replenishes itself.

“Blending,” or “bypassing,” is oneengineering technique that many sew-

erage operators have used to handle peakflows. During wet weather, utilities route aportion of peak wastewater flows aroundthe biological treatment units, then com-bine the rerouted flows with the portion ofwastewater that went through biologicaltreatment. After blending, the effluent isusually disinfected and discharged intowater bodies.

For decades, environmental permittingagencies in some states have allowed sewer-age operators to use this technique in aneffort to avoid CSOs. Recently, however,

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blending has become a controversial practicedebated by the wastewater industry, environ-mentalists, and public health scientists.

The wastewater treatment industryargues that bypassing biological treatmentfor a portion of the water is a significantimprovement over releasing completelyuntreated wastewater, which is what hap-pens when combined sewers overflow. “Ifthe choice is between raw sewage gettingsent into waterways and wastewater gettingsent to the treatment facility, most peoplewould rather that the wastewater get treat-ment,” says Alexandra Dunn, generalcounsel of the National Association ofClean Water Agencies, a trade group repre-senting more than 300 utilities.

However, critics of blending say theprocess allows for a higher concentrationof pollutants to be released into water bod-ies, potentially sickening more people.When blending wastewater rather thanfully treating it, utilities are less effective atremoving microbial pathogens, saysCharles Haas, an environmental engineerat Drexel University. “It’s much more dif-ficult to disinfect poorly treated wastewaterthan fully treated wastewater, and I wouldconsider primary-treated wastewater aspoorly treated,” he says. Many solids maystill remain in primary-treated wastewater,and viruses, parasites, and bacteria withinthose solids are protected from disinfec-tion, he adds.

“When the wastewater industry talksabout blending versus CSOs, they arguethat blending is better in terms of protect-ing public health,” Rose says. “But I don’tthink they have the data on pathogens—viruses and parasites—to prove that. Muchmore research is needed on wastewater andon treatment to control pathogen risks.”

Toward Better Blending Nancy Stoner, director of the Clean WaterProject at the Natural Resources DefenseCouncil, says that current blending policyas outlined in the CSO Control Policy ischaotic and poorly regulated: “A lot oftreatment plants do blending [almost any-time it rains], and some are given the lee-way by states to do blending, while othertreatment plants are not given the leewaybut do it anyway.” In recent years, sewerageoperators have sought guidance from thefederal government on the blending issue.

In November 2003, the EPA proposeda new federal policy that would haveauthorized municipal sewage plants aroundthe country to blend wastewater in certaincircumstances and under certain condi-tions—for example, only during periods ofheavy rain or snowmelt, and only if plantswere already meeting effluent standards

required for permitting. The EPA said thatits proposed policy was already commonpractice in many communities.

During the public comment period,the EPA received about 98,000 comments,and the proposal was not warmlyembraced by environmentalists. “EPA’sproposal would put more partially treatedsewage into the environment,” says Stoner.“The solution to overflows is not tobypass, but to fix the leaky sewer systems.”

Congress reacted, too. On 3 March2005, members of the House of Repre-sentatives introduced bipartisan legislation,the “Save Our Waters From Sewage Act,”to block the EPA blending proposal. Thelegislation called for amendments to theClean Water Act to “prohibit a publiclyowned treatment works from divertingflows to bypass any more of its treatmentfacility unless the bypass is unavoidable . . .[and] there is not a feasible alternative tothe bypass.”

On 19 May 2005, the EPA announcedthat it would not finalize the sewage blend-ing policy as proposed in November 2003.“Blending is not a long-term solution,”said Benjamin Grumbles, assistant admin-istrator for the Office of Water, in a pressrelease at the time. “Our goal is to reduceoverflows and increase treatment of waste-water to protect human health and theenvironment.” The agency also said it willcontinue to review policy and regulatoryalternatives to create feasible approaches totreat wastewater.

The Cost of Fixing SystemsAccording to the EPA’s 2000 CleanWatersheds Needs Survey, it would costabout $50.6 billion over the next 20 yearsto reduce the nation’s CSO volume by85%. In recent years, some communitieswith CSOs have increased sewer rates toraise funds to upgrade their infrastructure.But it’s difficult for many localities to payfor large-scale sewer and water treatmentfacilities without federal and state aid, saysDunn. Some relatively prosperous commu-nities such as Grand Rapids, Michigan, arein the process of installing separatestormwater pipes, she adds, but this is notfeasible for large, financially distressedcities such as Detroit.

Municipalities, sewerage operators,public health scientists, and environmental-ists are calling for more federal funding toreplace aging pipes and upgrade treatmentsystems. But federal spending for sewerageinfrastructure is actually falling. During fis-cal year 2005, Congress cut $250 millionfrom the Clean Water State RevolvingFund (CWSRF), which provides low-costloans primarily for sewerage infrastructure

upgrades. In President Bush’s fiscal year2006 budget proposal, this fund faces a fur-ther one-third reduction.

Even in the best of fiscal times, theCWSRF, distributed among 50 states, can-not address municipal needs to borrow forCSO projects and repay on favorable terms.“In most cases,” says Dunn, “the total allo-cation to a state per year could be used byone city alone for one phase of its project.”For example, she says, the first phase of theCSO program in place at Narragansett Bay,Rhode Island, will cost $250 million,which could use up all of Rhode Island’sannual portion of the CWSRF.

Despite falling federal aid, communi-ties still—as mandated by the CSOControl Policy—must establish and find away to implement long-term control plansthat will provide for full compliance withthe Clean Water Act, including significantreduction of CSOs. Communities are invarious stages of developing and imple-menting their long-term plans.

Some cities such as Boston, Chicago,and Atlanta have built deep storage tunnelsto hold stormwater overflows, says ChrisHornback, regulatory director of theNational Association of Clean WaterAgencies. Eventually, the extra wastewatercan be treated at a flow that works for aparticular wastewater plant. “Buildingthese storage tunnels is a simple, straight-forward process, but it costs hundred andhundreds of millions of dollars, and atsome point you reach a break point incost,” he says.

Environmentalists call for less costlymethods of reducing stormwater runoffand CSOs. Such methods, says Stoner,include better means of trapping storm-water before it reaches sewers and puttingit into the ground instead. Installing raingardens, permeable pavements, roof gar-dens, or even just grassy swales or ditchesalong roadways can be beneficial for anumber of reasons: soil and vegetation pro-vide filtration, groundwater supplies arereplenished, and overland stormwaterflows are diminished. Such methods aremostly low-tech and cost-effective. [Formore information on reducing runoff, see“Paving Paradise: The Peril of ImperviousSurfaces,” p. A456 this issue.]

Even so, low-impact techniques alonewill not be enough to fully control theCSO problem, according to the EPA’s2004 report. Environmentalists andmunicipalities agree that, contrary to thecurrent trend, the answer will depend ongreater federal investment in wastewaterinfrastructure around the country.

John Tibbetts

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