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Those lessons learned are reflected inthese articles.

Part I also kicks off a new BioCycleeditorial feature in 2008, “OperatorInsights.” Appearing in every otherissue, Operator Insights will examinetopics that site managers face in theirdaily operations.

WHAT’S THE PROBLEM?In a nutshell, contamination. By

virtue of some of the data collected inannual storm water runoff monitoringrequirements on composting facilities— imposed under the Phase 1 Nation-al Pollutant Discharge EliminationSystem (NPDES) program establishedin the 1990s — it is now apparent thatrain falling on exposed compostingwindrows can pick up substantialamounts of pollutants. If discharged toreceiving streams unmanaged, the

pollutants have the po-tential to cause waterquality problems inthose streams. Theseoff-site losses present ahigher level of concernthan a similar amountof the same compoundsin the compost itselfbecause water qualitystandards for someconstituents (i.e. pesti-cides, metals) are setat much lower levelsthan any standards forland application ofcompost containingthese compounds andelements (Cole, 1994).

Not surprisingly, theconstituents in com-posting pad storm wa-ter runoff depend, tosome extent, on thefeedstocks being com-

posted. Yard trimmings compostingfacilities have long been thought tohave the least potential for contami-nation due to the relatively clean na-ture of the feedstocks, i.e., leastamount of chemical and pathogeniccontamination to start with (relative tomanure, biosolids and food scraps). Yet

ONE OF the clearly recognizedbenefits of compost when usedas a soil amendment is its abil-

ity to increase the water holding ca-pacity of the soil. This is due to theability of compost to retain water.Yet, this same beneficial material,while being manufactured, is nowbelieved to create water qualityproblems that require regulatorypermitting and potentially expen-sive treatment systems. Unfortu-nately, there is a wide variety ofstate regulatory approaches to ad-dress this issue; some regulatestorm water runoff from compost-ing pads as a wastewater, and someregulate it as storm water.

The purpose of this two-part arti-cle is to examine how storm water isproduced at a composting facility,what types of contaminants it mighthave, how is it being regulated andwhat types of treatment work tomeet regulatory requirements. As aformer composting facility operatorand state organics recycling coordi-nator, and now as a consultant, Ihave worked first-hand on calculat-ing storm water flows, identifyingpollutants, and determining the op-timum management strategy.

ManagingStormWaterIs it storm water? Is it wastewater? What isthe best method to calculate flows at the site?These questions, and more, are answered inBioCycle’s new Operator Insights feature. Part I

Craig Coker

Taking a manual grabsample of runoff (left) atthe wrong time mayresult in pollutantconcentrations that arenot truly representative.

Sampling methods to offset this difficulty include flow-composite and time-composite samples, often collectedwith automated sampling equipment (above).

28 BIOCYCLE FEBRUARY 2008

ADVANCING COMPOSTING, ORGANICS RECYCLING& RENEWABLE ENERGY

419 State Avenue, Emmaus, PA 18049-3097610-967-4135 • www.biocycle.net

Reprinted With Permission From:February, 2008

BIOCYCLE FEBRUARY 2008 29

runoff from these facilities has beenshown to be highly variable, containingpotentially significant levels of nutri-ents, soluble salts, Biological and Chem-ical Oxygen Demand (BOD/ COD), tan-nins and phenols from decomposingleaves, herbicides, pesticides, fungicidesand fecal coliform (probably from animalfeces mixed in the yard trimmings). An-imal manure, biosolids and food scrapscomposting facility runoff will likelyhave higher levels of nutrients, organicacids produced during decompositionand fecal coliform bacteria (OregonDEQ, 2004). Little data is available onother pathogenic microorganisms incomposting facility runoff.

Potential impacts of these con-stituents on stream and river waterquality are the same as, and in some cas-es more severe than, untreated dis-charges of sanitary wastewater. BODand COD exert an oxygen demand on thedissolved oxygen in water, which if de-pleted will cause significant aquatic eco-logical mortalities. Widespread fish killsare the most obvious of these problems.Nutrients contribute to the geomorpho-logic process known as eutrophication,where nutrients support the growth ofalgae, which also deplete oxygen upontheir deaths, as well as stimulate thegrowth of vegetation (this is an accelera-tion of the natural process by which shal-low watercourses become swamps, andin turn, eventually become dry land).Tannins and lignins are natural dis-solved organic acids that give water thecharacteristic color of compost tea. Phe-nols are a group of related acidic com-pounds that are hydroxyl derivatives ofaromatic hydrocarbons. These includesuch substances as cresol, catechol,quinol, xylenol, guaiacol and resorcinol.There are two effects apparent in phe-nol-contaminated waters: toxicity toaquatic life and the generation of an un-pleasant taste in fish and shellfish.

There are different sources of watercontributing to runoff from a compostingfacility and each is subject to different lev-els of potential contamination. Orderedfrom most to least potential for contami-nation, they are: leachate, process stormwater, nonprocess storm water, wash wa-ter and run-on. “Runoff” is generally amix of leachate, process storm water,wash water and nonprocess storm water.Each has different characteristics, as de-fined below, and should be managed toprevent potential environmental harm.

In most composting piles, water movesto the bottom under the influence ofgravity and creates leachate if the mois-ture content of the compost exceeds itswater holding capacity (Krogmann,2000). Moisture content in a pile is af-fected by feedstock types, mixing proce-dures, incoming rainfall, decompositionrates of organic matter that release the

water bound inside plant and animal cellwalls, the presence or absence of forcedaeration that tends to evaporate moremoisture and whether the compostingprocess uses supplemental irrigationduring active composting. A morecoarsly textured mix, like yard trim-mings, will have less water holding ca-pacity than a more finely textured mix,such as dairy manure bulked with saw-dust. Leachate draining through a com-posting pile will pick up soluble materi-als (tannins, nutrients, salts) as well assmall particulate matter created by thedecomposition process. It is a combina-tion of the tannic acids and the particu-late matter that give leachate its char-acteristic dark brown color.

Process storm water is precipitationthat falls on the site and contacts thecomposting material without flowingthrough the pile. This includes runofffrom the sides of the pile as well as stormwater that comes in contact with wastematerial and compost that has strayedfrom the pile. Nonprocess storm water isprecipitation that falls on the compostsite, but that doesn’t come into contactwith wastes or compost. Wash water isgenerated by washing vehicles andequipment and contains materials dis-lodged from vehicle wheels and bodies,but the concentrations tend to be lowerdue to the high volumes of dilutive waterused in washing. On the other hand,wash waters can contain surfactantsand other chemicals from any washingdetergents used. Run-on is rainfallrunoff from uphill of the composting sitethat flows through the site and comes incontact with wastes or compost. En-closed composting facilities also havecondensate — water that evaporatesfrom the compost and condenses on cool-er surfaces such as building walls.

HOW MUCH RUNOFF?Figuring out how much storm water

runoff will have to be managed at a com-posting facility is not an exact science.Rainfall varies in intensity both in spaceand in time, as evidenced by the intensi-ty of a thunderstorm on one side of aroad, but not on the other. Similarly,runoff quantities vary as a function ofhow much rain has fallen recently, pos-sibly saturating the ground, as well asconstructed conditions like compostingpad construction materials; presence,orientation, spacing and age ofwindrows; and moisture content in thosewindrows. A 2004 Canadian study con-cluded that about 68 percent of the in-coming rainfall became runoff atwindrow composting facilities, and thatthere was a significant delay betweenrainfall and runoff as the compost de-tained the rainfall and released it slowlyover a period of one to two days (Wilson,2004).

Quantities Of Storm WaterThere are several tools of hydrology

and hydraulics available to calculaterunoff quantities from various stormevents. Storm water management reg-ulations and programs have historical-ly been focused on managing quantitiesof storm water. These rules are oftenbased on what is called the “recurrenceinterval” of a storm; terms such as “25-year, 24-hour” and “10-year, 1-hour”storms are often used.

The recurrence interval of a storm isa statistical abstract, and mathemati-cally is the inverse of its probability ofoccurrence in any given year. For ex-ample, a “25-year” storm has a statisti-cal probability of occurring once every25 years (the inverse is 1/25, whichequals 0.04, or 4 percent). Thus the 25-year storm has a 4 percent chance of oc-curring in any given year. Similarly, a10-year storm has a 10 percent chanceof occurrence and a 100-year storm hasa 1 percent chance of occurrence. It isworthwhile to note that these statisti-cal abstractions can be misleading.Many people think that if a storm hasonly a 4 percent chance of occurring(i.e. once every 25 years), it is unlikelyto occur more frequently. It is entirelypossible that two 25-year storms canoccur in the same year, or even in thesame week or month.

A “24-hour” storm is the totalamount of precipitation that falls in24 hours, which, for example, is 6.5inches here in western Virginia. Simi-larly, a one-hour storm is the amountof rain falling in one hour (about 2.2inches here). However, storm watermanagement systems are based onboth volumes of storm water as well asflow rates of water to be managed, soa storm of one hour duration with arainfall intensity of 1.5 inches perhour will produce the same volume ofrain (1.5 inches) as a storm of six hourduration but only one-quarterinch/hour rainfall intensity. That 1.5inches of rain will produce a volume of54,450 cubic feet of rainfall (about407,000 gallons) on a 10-acre concreteor asphalt composting pad. Not all ofthat rain becomes runoff.

Flow rates are measured in volumesper unit of time (for example, cubicfeet per second, or cfs). Flow rates ofrunoff from a storm vary over the du-ration of the storm and are character-ized by hydrographs, which plot thechange in runoff flow rate over timefor a given storm. Figure 1 is a runoffhydrograph for a 10-year, 1-hourstorm of 2.2 inches/hour falling on13.25 acres of gravel compost paddraining to a pond. This storm willproduce a peak discharge of 14.13 cfsand a runoff volume of 18,274 cubicfeet (136,690 gallons).

30 BIOCYCLE FEBRUARY 2008

Calculating A Runoff Curve Or Coefficient

Figuring out how much of the rainfalling becomes runoff to be managed ina storm water system requires an esti-mation of the absorptive capacity of thesurface onto which that rain falls. In aforested watershed, rainfall is intercept-ed by leaves and infiltrates into theground, so only a portion becomes runoffthat reaches streams. In an asphaltparking lot (or composting pad), little isintercepted or infiltrated, so most of it be-comes runoff (but not all, as even asphaltor concrete will intercept small amountsof rain in surface irregularities).

Dimensionless numerical coefficientshave been developed to represent dif-ferent surface conditions affectingrunoff. The exact number used dependson the method of hydrological analysis— whether it is hydrograph-based ornonhydrograph-based. Table 1 presentsrunoff coefficients for different landuses (or “cover types”) for both nonhy-drograph methods and for hydrograph-based methods (Virginia DCR, 1999).Generally speaking, land uses that

have higher amounts of impervious sur-face have higher runoff coefficients, re-flecting that more of the incoming rain-fall is being converted to outgoingrunoff and less is lost to interceptionand infiltration.

Hydrologic soil groups are assignedby the U.S. Department of Agricultureand reflect the “runoff potential” of aparticular soil. For example sandysoils tend to be in Groups A and B (seeTable 1 categories), while clayey soilstend to be in Groups C and D, whichhave higher runoff potential.

Calculating a runoff curve number orcoefficient for a composting pad re-quires use of a weighted average ap-proach (weighted by the percentage ofthe pad occupied by windrows and thepercentage not covered with windrows).The total square footage of the pad oc-cupied by windrows has a lower valuethan the total square footage of the padbetween windrows. Not all compostingwindrows have the same runoff coeffi-cient. Drier compost, subject to summertemperatures and lighter rain intensi-ty, would likely result in a lower mea-sured runoff coefficient. For an asphaltcomposting pad, assume a coefficient of0.85 for the aisle spaces betweenwindrows. For the windrows them-selves, assume a coefficient between0.50 and 0.70 (Kalaba, et al., 2007).

The most widely used nonhydro-graph method for calculating runoff isthe Rational Method. It was developedin 1889 as a method for calculatingpeak flows for sizing storm drains:

Q = C x I x Awhere Q = maximum rate of runoff, in

cubic feet per secondC = a dimensionless runoff coef-

ficient (see Table 1)I = the design rainfall intensity,

in inches per hour, for a duration equal

to the time of concentration of the watershed

A = the drainage area, in acresThe term “time of concentration”

refers to the time it takes for runoff tomove from the most hydrologically dis-tant point in the drainage area to thepoint of interest, such as the inlet to astorm pond, a flow monitoring stationon a stream or the design location for anew impoundment. For paved com-posting pad runoff calculations, time ofconcentration is measured in minutes,provided upgradient runoff is properlydiverted around the pad. For naturalwatersheds, time of concentration ismeasured in hours.

There are a number of limitationswith the Rational Method in determin-ing runoff volumes and flow rates: it as-sumes the duration of the design stormis equal to the time of concentration inthe drainage area; it fails to account forthe fact that compost windrows can shedrainfall, absorb rainfall or act as a reser-voir and detain rainfall; and it assumesthat the fraction of rainfall that becomesrunoff is independent of rainfall intensi-ty or volume (with windrows of compost,runoff varies with rainfall intensity),along with others (Kalaba, 2007).

Using the Rational Method on thesame composting facility illustrated inFigure 1 (i.e. drainage area = 13.25acres, rainfall intensity = 2.2 in/hr) andassuming a weighted runoff coefficientof 0.75, the calculated peak dischargerate is 21.86 cfs, a 54 percent overesti-mate compared to the more rigorousand accurate hydrograph methodshown in Figure 1. This might have re-sulted in expensive overdesign of astorm water management system.

Developing an accurate natural hy-drograph of a storm event requires ex-tensive real-time flow monitoring. Giventhe cost and difficulty of real-time moni-toring of small watersheds, syntheticunit hydrographs were developed bySnyder in 1938 to establish a method ofsimulating a natural hydrograph by us-ing watershed parameters (area, shape,slope and ground cover) and storm char-acteristics. The synthetic unit hydro-graph method is the cornerstone of thehydrologic work done by the USDA’s SoilConservation Service (now the NaturalResources Conservation Service), em-bodied in the National EngineeringHandbook, Section 4, Hydrology (1985)and in widely-available computer mod-els like TR-20, “Project Formulation, Hy-drology” (1982) and TR-55, “Urban Hy-drology for Small Watersheds” (1986).

TR-55 presents two general methodsfor estimating peak discharges from ur-ban watersheds: the graphical methodand the tabular method. The graphicalmethod is limited to watersheds whererunoff characteristics are fairly uniform

Figure 1. Royal Oaks site peak runoff

15

12

9

6

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00 10 20 30 40 50 60 70 80

15

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0

Time (minutes)

Runoff hydrograph for a 10-year, 1-hour storm of 2.2inches/hour falling on 13.25 acres of gravel compost paddraining to a pond

Cubic feet per second

Table 1. Runoff coefficients

Nonhydrograph Method Hydrograph MethodRational Method Runoff Coefficients Runoff Curve Numbers for Urban Areas

Hydrologic Soil GroupLand Use “C” Value Cover Type A B C D

Business, industrial and commercial 0.90 Paved parking lots 98 98 98 98Apartments 0.75 Paved streets 83 89 92 93Schools 0.60 Gravel streets 76 85 89 91Residential – lots of 10,000 sq. ft. 0.50 Residential – 1/8 acre 77 85 90 92- lots of 12,000 sq. ft 0.45 Residential – 1/4 acre 61 75 83 87- lots of 17,000 sq. ft 0.45 Residential – 1/2 acre 54 70 80 85- lots of 1/2 acre or more 0.40 Residential – 1 acre 51 68 79 84Parks and unimproved areas 0.34 Newly graded areas 77 86 91 94Paved and roof areas 0.90 Pasture or grassland 39 61 74 80Cultivated areas 0.60 Meadow 30 58 71 78Pasture 0.45 Farmsteads 59 74 82 86Forest 0.30 Woods- grass combo 32 58 72 79Steep grass slopes (2:1) 0.70 Woods 30 55 70 77Shoulder and ditch areas 0.50 Open Space (parks, lawns) 39 61 74 80Lawns 0.20

BIOCYCLE FEBRUARY 2008 31

and soils, land use and ground cover canbe represented by a single Runoff CurveNumber (see Table 1 for examples). Thegraphical method provides a peak dis-charge only and is not applicable for sit-uations where a hydrograph is required.The tabular method is a more completeapproach and can be used to develop ahydrograph at any point in a watershed.

There are a number of other comput-er-based storm water hydrologic andwater quality models available, such asthe U. S. Environmental ProtectionAgency’s Storm Water ManagementModel (SWMM), which is a comprehen-sive computer model for analysis ofquantity and quality problems associat-ed with urban runoff. Both single eventand continuous simulation can be per-formed on catchments having stormsewers, or combined sewers and naturaldrainage, for prediction of flows, stagesand pollutant concentrations. Thesemodels tend to be watershed-scale mod-els, rather than site-scale models.

WHAT’S IN THE RUNOFF?Sampling Methods and Tools

Sampling of storm water for laborato-ry analysis and characterization is con-siderably more difficult than samplingprocess wastewaters coming out of theend of a pipe, because of the lack of con-trol over sampling times and conditions.Rainfall events often occur at night, onweekends and holidays, and sometimeswith little advance notice. It is also diffi-cult to obtain a truly “representative”sample. For example, the storm waterdischarge permit issued by the MissouriDepartment of Natural Resources to aprivate composter requires sampling“during a storm water event of 0.1 inchor greater and during the first 30 min-utes of the discharge.” This is meant tocapture the “first flush” of pollutantsswept up by runoff, which is obviouslymeant to capture a “worst-case” situa-tion. Taking a one-time sample of runoff(known as a “grab” sample) at the wrongtime may result in pollutant concentra-tions that are not truly representative.

Sampling methods to offset this diffi-culty include flow-composited and time-composited samples, often collectedwith automated sampling equipment. Aflow-proportional composite sampleconsists of discrete samples collected ata rate proportional to flow. Taking flow-composited samples requires knowingthe flow rate of the watercourse, whichis normally done by inserting a tempo-rary calibrated V-notch weir in thechannel. A time composite sample con-sists of discrete samples collected atconstant time intervals.

Actual procedures used to obtain goodquality representative samples are im-portant. Recommended procedures in-clude: wear disposable, powder-free

gloves; grab samples with the storm wa-ter entering directly into bottles provid-ed by the laboratory (don’t transferthem from other containers that may becontaminated with phosphorus-baseddetergent residue); sample where thewater has a moderate flow and someturbulence, if possible, so that the sam-ple is well-mixed; do not overfill the bot-tle so as not to wash out any samplepreservative provided by the laboratory(normally used for ammonia and phos-phorus); and cap and label the bottle assoon as the sample is taken (Washing-ton DOE, 2005).

If samples are to be analyzed for bio-logicals (fecal coliform, otherpathogens), the same sample preserva-tion and shipping issues that affectcompost samples will affect these wa-ter samples. Refrigerate the sampleimmediately after collection and ship itto the laboratory using an overnightservice, packing the sample in iced gel-packs, or the equivalent.

Pollutant ConcentrationsPollutant concentrations in runoff

from composting facilities vary widely. A1997 study by the Clean WashingtonCenter characterized runoff from fourcomposting facilities in the PacificNorthwest, which is shown in Table 2(CWC, 1997). Another study (Krog-mann, 2000) monitored storm waterquality for three years at a Europeancomposting facility handling residentialsource-separated organics. The resultsof that monitoring are shown in Table 3.

The BOD5/COD5 ratio is a measure ofthe biodegradability of a wastewater. ABOD5/COD5 ratio of 0.5 is the same or-der of magnitude as municipal wastew-ater and is considered easily degradable.A wastewater with a BOD5/COD5 ratioless than 0.1 is considered biologicallydifficult to degrade. The BOD5/COD5 ra-

tio of the runoff from the large-scale openwindrow facility in Krogmann’s studyranged between 0.02 (minimum) and0.37 (maximum) with a geometric meanof 0.05, suggesting it is a wastestreamthat may be difficult to biodegrade. �

Craig Coker is a Contributing Editor toBioCycle and a Principal in the firm ofCoker Composting & Consulting inRoanoke, Virginia. He can be reached at(540) 904-2698 or by email at craigcok-er@cox.net. Part 2 of this article, to be pub-lished in April 2008, will discuss struc-tural and operational management optionsfor managing storm water quality and thestorm water permitting programs and is-sues affecting the composting industry.

REFERENCES – PART 1Clean Washington Center, “Evaluation of

Compost Facility Runoff for BeneficialReuse,” prepared by E & A Environmen-tal Consultants, May 1997, p. 11.

Cole, M.A., “Assessing the Impact of Com-posting Yard Trimmings,” BioCycle, Vol.35, No. 4, April 1994, p. 92.

Kalaba, L., et al., “A Storm Water RunoffModel for Open Windrow CompostingSites,” Compost Science & Utilization,Vol. 15, No. 3, p. 142-150.

Krogmann, U., “Selected Characteristics ofLeachate, Condensate, and Runoff Re-leased During Composting of BiogenicWastes,” Waste Management and Re-search, Vol. 18, 2000, p. 235-248.

Oregon Department of EnvironmentalQuality, “Commercial Composting Wa-ter Quality Permit Development,” pre-pared by CH2MHill, May 2004.

Virginia Department of Conservation andRecreation, “Virginia Storm waterHandbook,” 1999, Sec. 4, HydrologicMethods.

Washington Department of Ecology, “Howto do Storm water Sampling – A Guidefor Industrial Facilities,” Publication 02-10-071, Dec. 2002, revised Jan. 2005.

Wilson, B.G., et al., “Stormwater RunoffFrom Open Windrow Composting Facil-ities,” Journal of Environmental Engi-neering Science, Vol. 3, 2004, p. 537-540.

Table 2. Runoff ranges from four facilities

Parameter Range(mg/l)

BOD5 20 - 3,200Total solids 1,100 - 19,600Volatile solids 430 - 9,220Color (color units) 1,000 - 70,000Fecal (MPN/100ml) 200 - 24,000,000Copper (ppb) 33 - 821Zinc (ppb) 107 - 1,490Nutrients:Ammonia N 32 - 1600Total Kjeldahl N 14 - 3,000Nitrate+nitrite N 0 - 8

Total phosphorus 4 - 170Ortho phosphate 0 - 90pH (standard units) 6.7 - 9.5Conductivity 887 - 16,500Chloride 52 - 2,100Potassium 167 - 4,640

Table 3. Analysis of runoff from openwindrow composting facilities (30 samples)

Parameter Range(mg/l)

Arsenic (As) 0.001 – 0.044Lead (Pb) <0.001 – 0.500Cadmium (Cd) <0.001 – 0.172Zinc (Zn) 0.011 – 2.4Ammonium (NH4

+-N) 2.0 – 46.0Nitrate (NO3-N) <0.1 – 96.4Nitrite (NO2-N) <0.1 – 0.80Chlorides 106 – 445BOD5 <2.0 – 513COD5 56 – 1768BOD5/COD5 ratio 0.02 – 0.37

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compost runoff are heavy metals, oiland grease, and tannins and phenols.Tannins and phenols are derived fromthe woody materials used in compost-ing, and are derivatives of aromatichydrocarbons which, if discharged un-treated, have potentially significantimpacts on aquatic life.

Oxygen-demanding substances inwastewater are normally measuredusing two surrogates — BiologicalOxygen Demand (BOD) and ChemicalOxygen Demand (COD). BOD is nor-mally defined as the amount of oxygenrequired by bacteria while stabilizingdecomposable organic matter in waterunder aerobic conditions. COD is de-fined as the total quantity of oxygenneeded to completely oxidize all or-ganic matter to carbon dioxide and wa-ter. COD values are usually higherthan BOD values and may be muchgreater when significant amounts ofbiologically resistant organic matter(like lignin in wood fibers) are present.Consuming the dissolved oxygen inwaterways has significant adverse ef-fects on aquatic life. Suspended solidswashed into streams can blanket andsmother bottom-dwelling aquatic lifeas sediments settle. These solids canalso interfere with light transmissionand aquatic vegetation photosynthesisif they remain suspended. In addition,

they often carry adsorbed oxygen-de-manding substances into the water,which cause odor problems as dis-solved oxygen levels fall.

Nutrients of importance in waterpollution control are the water-solubleforms of nitrogen (ammonia, nitratesand nitrites) as well as phosphorus.These can stimulate the growth of al-gae in water, which create their ownoxygen demands on waters when theydie, and ammonia is toxic to aquaticlife in sufficient quantities. Contami-nation of waters with fecal coliform isone of the principal reasons why somewaters have lost their “fishable,swimmable” status. Tannins, phenolsand similar substances are not onlytoxic in their own way, but consumedissolved oxygen as they degrade toless complex forms.

Heavy metals such as chromium,copper, lead and zinc are a concern instorm water runoff from urbanized ar-eas, and can be a concern in compost-ing facility runoff, particularly from fa-cilities handling industrial or biosolidsfeedstocks. As the majority of com-posting facilities process feedstockswith limited heavy metals, and multi-year sampling at some facilities indi-cates no migration of heavy metals incompost facility runoff, these are pol-lutants of largely secondary considera-tion in developing water pollution con-trol strategies for composting facilities.

REGULATORY APPROACHESPart 3 of this series (to run in May

2008) will look at how storm waterfrom composting facilities is being reg-ulated. Most states in the U.S. havedelegated authority from the U.S. En-vironmental Protection Agency to reg-ulate point and nonpoint sources ofwater pollution. Permits issued bystate environmental agencies regulatethe quantities of pollutants allowed tobe discharged. These allowable quan-tities are converted to concentrationsin the discharge (which are easier tomeasure for compliance) based on al-lowable quantities of water flow. Thisapproach works well with traditionalend-of-pipe discharges from installa-tions where water flow is predictableand relatively consistent.

Water flows in storm water runoffare considerably more unpredictable.There is a varying assortment of con-trol strategies in use by states for con-trolling potential water pollution fromstorm water runoff at composting fa-cilities. For example, Oregon has de-veloped a customized storm water per-

WATER quality regulationshave expanded from individ-ual end-of-pipe point sources

to include runoff-generated areanonpoint sources of water pollu-tants. This has led to increasedscrutiny of water pollution potentialfrom rainfall-induced runoff at com-posting facilities. While all typesand configurations of composting fa-cilities are being examined, the ma-jority of attention is on the main-stream technology of open-airturned windrow systems, whererainfall comes into contact withwaste materials, composting pilesand finished compost products.

Part 1 of this series (February2008) looked at the quantity andquality considerations of this runoff.The amount and data quality ofchemical and biological characteri-zation data for storm water runoff israther limited; however, availabledata suggests that compost pileleachate and runoff contaminatedwith leachate have levels of tradi-tional water pollutants that canexceed levels found in standard do-mestic wastewater. These pollu-tants include oxygen-demandingsubstances, suspended solids, nutri-ents and bacterial contamination.Other pollutants of importance in

StormWaterTreatmentSegregating storm water flows at compostingfacilities to minimize generation of highlycontaminated runoff goes a long way to reducingtreatment costs. Part II

Craig Coker

BIOCYCLE APRIL 2008 29

30 BIOCYCLE APRIL 2008

mitting program for composting facili-ties. North Carolina, on the other hand,has decided not to issue any storm waterpermits for composting facilities, in-stead making facilities get wastewaterdischarge permits. Several states usethe Multi-Sector General Permit ap-proach used for industrial facilities,choosing to regulate composters underthe SIC Code for Fertilizer Mixing (SIC2875). Others have no regulations at all.It is becoming increasingly clear, how-ever, that composting facilities mustplan for control and management ofstorm water through a combination ofboth structural and nonstructural man-agement techniques.

REDUCE, REUSE, RECYCLE

ReduceReducing the quantities of storm wa-

ter to be managed is the first step. Un-der the conditional no exposure exclu-sion, operators of industrial facilities inany of the categories of “storm waterdischarges associated with industrialactivity,” may have the opportunity tocertify to a condition of “no exposure” iftheir industrial materials and opera-tions are not exposed to storm water.At least one in-vessel composting oper-ation in North Carolina is pursuingthis to avoid permitting. Several waterquality regulators interviewed for thisseries of articles expressed a desire tosee new composting facilities enclosedin buildings, and existing facilitiesretrofitted with roofed structures tokeep rainfall from compost piles.

Another method of reducing the quan-tity of “contaminated” storm water isthrough segregation of runoff flows tominimize the quantities of waters withthe highest degree of contamination (i.e.leachates). Strategies include site grad-ing to divert up-gradient runoff around acomposting facility, using design andconstruction techniques to segregateleachate from storm water (see “EnzymeProducer Grows Greener With Compost-ing,” BioCycle December 2006) and iso-lating vehicle and equipment washingstations with their own runoff contain-ment. By segregating water flows, costsfor treating highly-contaminatedwastewaters can be reduced and less ex-pensive Best Management Practices(BMPs) and pollution prevention mech-anisms can be used for managing lightlycontaminated storm waters.

Storm Water Pollution PreventionPlans (SWPPP) are another widely usedmechanism to reduce pollutants instorm water. While more specifics areprovided in Part 3 of this series, a SW-PPP includes: a facility assessment;identification of areas of potential or pastpollution discharge; a monitoring (sam-pling and visual inspection) plan; a

schedule for implementing additional orenhanced BMPs; a list of operational andstructural BMPs; and development ofoperation and maintenance procedures(Washington DOE, 2004).

ReuseThe most feasible method of reusing

collected storm water is to reintroduce itto the compost piles to keep moisturecontents at the optimum 50 to 55 per-cent level. Windrows can be “irrigated”with hoses, sprinklers or water trucks.As compost piles have considerable wa-ter-absorptive capacities, a substantialamount of water can be reused this way.Table 1 shows a sample calculation ofhow much water can be reused for oneirrigation event. Assumptions used inthis example include: Facility capturesand holds the 25-year, 24-hour storm(6.62 inches for coastal mid-Atlanticstate); all up-gradient runoff is divertedaround composting facility; capture andcontain runoff from 8-acre compost pad;all windrows are covered with fabric andare impermeable; site soils are in Hy-drologic Soil Group A or B.

In this example, the windrows are cov-ered with fabric blankets. Openwindrows will produce much less runoffto be managed due to absorption of rain-water into the windrow (see Part 1 ofthis series). While the above method isbased on computing the weight of waterto be added (and then converting that

back to gallons), another formula for cal-culating the maximum volume of waterthat can be added to compost piles is(The Composting Association, 2007):

VL = VM x dM x (MCmax – MCM) x 1000100 x dL

where:VL = volume of water to be added

(litres)VM = total volume of composting ma-

terial (cubic metres)dM = bulk density of composting mate-

rial (tonnes/cu. meter)MCmax= target moisture content, per-

cent (usually 55%)MCM= starting moisture content of

pile, percentdL= density of water (tonnes/cu.

meter)Because there is some risk that the

collected storm water will have fecal co-liform contamination, irrigation withstorm water should not be done after acompost pile reaches the Process to Fur-ther Reduce Pathogens (PFRP) time-temperature standard unless that wa-ter has been disinfected. Otherwise,there is a risk of reinoculating a finishedcompost pile with viable pathogens.This is true even if only yard trimmingsor vegetative debris are being compost-ed, as monitoring data has shown ele-vated levels of fecal coliform in runofffrom yard trimmings compost facilities.This fecal contamination is presumably

Table 1. Example storm water reuse calculation

Calculate runoff curve number for siteArea occupied by windrows = 35 windrows, each 14’ wide x 400’ long 196,000 SFArea open 152,480 SFTotal windrow area 348,480 SFAssumed curve numbers (CN)1 Windrows (impervious) 98

Open areas (packed earth) 85Weighted average CN = 92.3

Amount of runoffPer USDA NRCS rainfall-runoff tables:6.62” of rain falling on a CN= 92.3 produces 5.76 inches

Volume of runoff to be controlledRunoff amount 5.76 inchesRunoff linear volume (inches x area) 167,270 cubic feetRunoff liquid volume (1 CF = 7.48 gallons) 1,251,183 gallons

Quantity to be used in windrow irrigationAssume 50% of windrows are below PFRP and can be irrigatedAssume initial moisture content of windrows is 45% and end moisture level is 55%Material on pad: 17 windrows x 871 CY/windrow = 14,807 CY

Convert to weight @ 1200 lbs/CY = 8,884 tonsAmount of water @ 45% = 3,998 tonsAmount of water @ 55% = 4,886 tonsAmount of water to be added = 888 tonsVolume of water to be added (at 8.4 lbs/gal) = 211,529 gallonsAmount of water available - 1,251,183 gallons2

Excess irrigation water available = 1,039,654 gallons

1Dimensionless numbers that reflect the relative amounts of infiltration versus runoff 2Would have to be captured in a pond or tank for reuse

BIOCYCLE APRIL 2008 31

from animal fecesmixed in with theyard debris.

Disinfection ofcollected stormwater is possible,using a dosagerate of 5 to 25 mg/Lavailable chlorine(i.e. between 2 and6.5 ounces ofClorox® bleach per

100 gallons of water). The effectivenessof this depends on the suspended solidscontent of the storm water, and it mayhave adverse effects on the compostingprocess once used as irrigation water. Inaddition, some states may consider thisa “wastewater treatment process” forpermitting requirements.

Some composters are developing per-manent water reuse systems to managestorm water. At Royal Oak Farm, a 500-tons/day open-air turned windrow facili-ty in Evington, Virginia, a subterraneanirrigation system was built as part of anupgrade. This system serves both waterreuse and fire fighting purposes, andconsists of a series of 3-inch stanchions,or standpipes, around the perimeter ofthe four compost pads, fed by a networkof 6-inch PVC pipes. The system ischarged by two 30-HP electric pumps,where irrigating windrows is done withone pump in service, drawing water froma lined storm water pond on site. Bothpumps are used if fire fighting is needed;additional water can be drawn from aseparate farm pond. Royal Oak uses aBackhus windrow turner and a winduphose reel to connect the turner to the ir-rigation standpipes.

Recycle One way to recycle composting facility

runoff is to use it as irrigation water forcrops. These can include row crops, pas-tureland, turfgrass or biomass silvicul-

ture crops (such as hybrid poplar trees).Irrigation methods include overlandflow, a spray system, drip irrigation orusing subsurface infiltration galleries.Hydraulic loading is a primary designtool when using irrigation to recyclepurely storm water. Hydraulic loading,or how much water a field can absorb, isdefined by site-specific soil conditions,depths to seasonal high groundwater ta-bles and regional climate considerations(a water balance analysis of precipita-tion and pan evaporation).

Because composting facility runoffcontains nutrients, it is more likely to beregulated as a wastewater and be subjectto both nutrient and hydraulic loadingconstraints. Many states now requireland application systems to be based onNutrient Management Plans (NMPs),which are site- and field-specific assess-ments of the potential for nitrogen andphosphorus transport to surface waters.

Whether compost facility runoff isclassified as a “wastewater” or a “stormwater” is a legal question and has impli-cations for recycling via land application.Many states require some degree oftreatment of a “wastewater” prior to landapplication. For example, in Virginia,wastewater to be land applied must bepretreated to a maximum BOD level of60 mg/L and predisinfected to a maxi-mum fecal coliform level of 200 MPN/100ml. The degree of disinfection often in-fluences the size of the required bufferzone. In Washington, the setback re-quirement from property lines is 100 feetif the wastewater meets the disinfectionpre-application limit of 200 MPN/100 ml,but climbs to 650 feet if it does not.

TREATMENT STRATEGIES Traditionally, storm water manage-

ment has been about managing thequantity of water more than the qualityof that water. With the new focus onnonpoint source pollution, the emphasisis now on pollutant removal efficienciesof existing storm water quantity controlmeasures, like detention ponds, as wellon treatment devices now on the mar-ket, like storm water filtration systemsthat can be incorporated into a munici-pal storm drain network.

Best Management PracticesBMPs remain the cornerstone of

storm water management strategies,and many are very suitable for use atcomposting facilities. BMPs are prac-tices, procedures or structural controlsused to prevent or reduce adverse im-pacts to receiving waters. BMPs do thisby managing the quantity and quality ofthe storm water, the leachate from com-post piles and equipment washdownwastewater generated at a compostingfacility. BMPs can be structural, opera-tional or both. Structural BMPs are

physical improvements and treatmentsthat can control, treat and protect waterquality. Examples include bioretentionbasins, vegetated filter strips and con-structed wetlands. Operational BMPsfocus on pollution prevention activitiesand on operation and maintenance ofstructural BMPs.

The Oregon Department of Environ-mental Quality retained the consultingengineering firm, CH2MHill, to evaluatesuitable BMPs for composting facilitiesas part of the background research fordevelopment of the new Compost Facili-ty Storm Water Permit program (seePart 3 for more information on this per-mit). This study ranked 27 BMPs interms of space efficiency, odor control,cost, level of complexity, number ofbenchmark constituents potentially con-trolled and whether the BMP was bene-ficial for control of bacteria, lead and ni-trates (Oregon DEQ, 2004). Table 2 liststhe 27 BMPs evaluated. The study con-cluded that these BMPs were suitablefor use by composting facilities, withsome modifications of definitions to tai-lor them to composting. Oregon’s newcompost storm water permitting pro-gram requires the use of one or more ofthese BMPs for runoff that has not beenmixed with compost pile leachate. TheFiscal Impact Analysis estimated, fortwo hypothetical composting operations,total annual BMP costs (amortized capi-tal plus operation) of $87,900 to$114,100. Estimated impact on tippingfees varied from $1.61/ton to $9.10/ton(Oregon DEQ, 2008).

Table 2. BMPs evaluated by OregonDepartment of Environmental Quality

Oil water separatorGrading facility areasAppropriate site vegetationGraveling or pavingSediment basins or trapsBioswale or grassy swaleSoil filterWetlandHolding pond/detention basinSediment control w/ filter bermsSediment control w/ centrifugal devicesGranular filtration tanksSoil and plant systemsChemical treatmentCoagulation & sedimentationAeration & ozonationUnderground injection with pretreatmentDiversion with containment barriersLiner systemsCollection and reuseMinimize runoff through operating proceduresRoof structureMembrane, tarp or coverIndoor operationsElimination of standing waterPrompt processing of feedstocksShaping of piles

The Royal Oak Farm irrigation systemconsists of 3-inch stanchions around theperimeter of the four compost pads, fedby a network of 6-inch PVC pipes(above). The system serves as both awater reuse function, and for firefighting purposes (below).

Pho

tos

cour

tesy

of C

oker

Com

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& C

onsu

lting

32 BIOCYCLE APRIL 2008

Onsite TreatmentOn-site treatment alternatives are

complicated by several factors. The de-gree of treatment needed depends on theultimate disposition of the contaminat-ed storm water. Another factor is theneed for some form of flow equalization,as wastewater treatment systems oper-ate most efficiently under a relativelyconstant flow. As runoff varies withstorm intensity and amount of compost-ing pad occupied by windrows, a reten-tion basin of adequate size is needed up-stream of any treatment processes.

If the water is to be reused for crop ir-rigation via a spray field, then pretreat-ment (as noted above) is usually suffi-cient. If it is to be discharged, treatmentlevels depend on discharge permit lev-els. In a nutrient-sensitive waterwaysubject to water quality-based effluentlimitations, it is possible that storm wa-ter would have to be treated to ad-vanced (or “tertiary”) levels. Tertiary ef-fluent discharge concentrations aretypically on the order of 3 to 5 mg/LBOD, 3 to 5 mg/L TSS, 1 mg/L Total Ni-trogen and 1 mg/L Total Phosphorus.

The pollutants found in composting fa-cility storm water can be treated by sev-eral different “unit processes” or in com-bination “package plants.” Table 3 listssome of the various unit processes usedin wastewater treatment.

Aeration/oxidation is the process of re-ducing oxygen-demanding substances byraising dissolved oxygen levels. Mostsimply, this involves aerating a stormwater pond. Numerous types of pond aer-ators are on the market, but compostersshould seek models with the highest oxy-gen transfer rate. For example, in Table1, a pond could contain 1.25 million gal-lons after the 24-hour, 25-year storm. Ifthat storm water has a BOD concentra-tion of 100 mg/L, then the pond wouldcontain 1,044 lbs of BOD. One pond aer-ator on the market has an oxygen trans-fer rate of 6.8 lbs/hour, so that aerator

would have to run 153.5hours to consume the en-tire BOD in the pond (ne-glecting microbial uptakeand utilization of both oxy-gen-demanding organicmaterials and the dissolvedoxygen in the water).

Biological conversion isthe fundamental processused in activated sludgeand fixed-film wastewatertreatment systems (i.e. aer-obic lagoons), as well as theprocesses at work in biolog-ically-rich features like en-gineered wetlands, bio-retention basins, bio-swales, etc. Biological conversion will re-duce pollutant concentrations of BOD, fe-cal coliform, some heavy metals andnutrients. Bioretention ponds (alsoknown as rain gardens) are becomingwidespread in areas adopting Low Im-pact Development policies, and havebeen shown to remove significantamounts of pollutants from storm water.Figure 1 illustrates a conceptual crosssection of a bioretention pond.

Suspended solids are a common prob-lem in compost storm water systems dueto compost fines washed in with therunoff. Keeping solids out of storm wa-ter management systems provides sev-eral benefits: improves the efficiency ofother treatment processes, such as dis-infection; eliminates or reduces difficultmaintenance tasks in lined ponds; re-duces or eliminates the potential foranaerobic conditions to form in a pond orbasin (with accompanying malodors);and minimizes the potential for dis-charge of solids in the event of a pondoverflow. Use of Filtrexx™ compost-filled filter socks is an inexpensive wayto keep solids out of ponds.

Disinfecting storm water for eitherreuse in the compost pile, for recycling viaa spray field or for discharge permit com-pliance is difficult. The three primarymethods are adding chlorine-containingcompounds (like sodium hypochlorite),making and introducing ozone gas intothe water or passing the water through abank of ultraviolet lights for irradiation.All three methods are sensitive to the sus-pended solids levels in the storm water. Anew process for disinfecting storm wateris electrocoagulation, which was original-ly used for precipitating heavy metals outof wastewater. A 2004 pilot study on ur-ban runoff in Los Angeles showed a 99percent removal of total coliform, a 98percent removal of chromium, a 96 per-cent removal of copper and a 98 percentremoval of lead (Brzozowski, 2007).

Engineered wetlands may offer oneof the best alternatives for manage-ment of composting facility runoff.Wetlands have a higher rate of biolog-

ical activity than most ecosystemsand, as a result, are capable of trans-forming the conventional pollutantsfound in storm water into harmlessbyproducts, or into nutrients that canbe used to encourage higher levels ofbiological productivity (see sidebar).

Pump & HaulIn some cases, composting facilities

may have to consider “pump-and-haul.”Due to capacity restrictions at the localtreatment plant, and to extremely strictwater quality standards in the water-shed of a potable water reservoir, this isan alternative being considered for theDurham, North Carolina Yard WasteComposting Facility. North Carolinaregulations require the capture andmanagement of the runoff from the 24-hour, 25-year storm, which in the case ofDurham, is about 1.8 million gallons. At$0.15/gallon cost to pump, haul and dis-charge at a treatment plant, this couldbe a cost of $270,000 each time the pondhas to be emptied.

BOTTOM LINEWater quality management — along

with odor control and air emissions —maywell be another powerful impetus for newcomposting facilities to consider in-vesselsystems or enclosure in buildings. Newopen-air facilities likely will need to care-fully engineer sites to segregate storm wa-ter runoff into manageable amounts tolimit the quantity of highly contaminatedand associated high-cost treatment re-quirements. Existing facilities facing per-mit renewals in states with aggressivestorm water management programs like-ly will have to consider multiple manage-ment measures, including pollution pre-vention operational practices, andcombinations of water quantity and waterquality management facilities. �

Craig Coker is a Contributing Editor to Bio-Cycle and a Principal in the firm of CokerComposting & Consulting in Roanoke, Vir-ginia (www.cokercompost.com). He can bereached at (540) 904-2698.

Table 3. Water pollutants and treatmentprocesses

Water Pollutant Treatment Process

BOD/COD Aeration/oxidationBiological conversion

Suspended solids ClarificationFiltration

Fecal coliform Disinfection (Chlorine, Ozone, UV)Biological conversion

Nitrogen and phosphorus Biological conversionPrecipitation (phosphorus only)

Heavy metals PrecipitationAdsorption

8" Gravel3-5' Grass 2-4" Mulch

Filter fabric(or choking

stone)

Underdrain2'+ Distance

to water table

Fill soil mediaMix 85-88% Sand 8-12% Fines 3-5% OrganicDepth Trees/shrubs=3ft Grass=2ft

In situ soil

Water table

4" Washed Sand8" #57 Stone

3:1

Cappedclean out pipe

Overflowstructure

9-12" Ponding

Figure 1. Bioretention pond cross section

SO

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: NC

DE

NR

, 200

7

REFERENCES – PART 2Brzozowski, C., “Nontraditional Stormwa-

ter Treatment”, Stormwater, Vol. 8, No.6, Forester Press, September 2007.

North Carolina Department of Environ-ment and Natural Resources, Stormwa-ter Best Management Practices Manual,July 2007.

Oregon Department of EnvironmentalQuality, “Commercial Composting Wa-ter Quality Permit Development”, pre-pared by CH2MHill, Contract No. 044-04, May 2004.

Oregon Department of EnvironmentalQuality, “Chapter 340 Proposed Rule-making, Statement of Need and Fiscaland Economic Impact”, January 15,2008.

The Composting Association (UK), “Optionsfor management and control of compost

liquor and excessive rainfall conditions”,Information Sheet No. 37, August 2007.

Washington Department of Ecology, “Guid-ance Manual for Preparing/Updating aStormwater

Pollution Prevention Plan for Industrial Fa-cilities”, Publication Number 04-10-030,April 2004.

Whitney, D., et.al., “ Application of Engi-neered Wetlands in Storm Water Man-agement, Stormwater, Vol. 9, No. 1,Forester Press, January 2008.

BIOCYCLE APRIL 2008 33

THERE are two main types of engi-neered, or constructed, wetlands— the Free-Water-Surface (FWS)

wetland, which has a standing pool ofwater, and a Subsurface-Flow (SF)wetland, in which water lies below thesurface of the wetlands media (usuallygravel). FWS wetlands don’t work wellin northern cold regions, but SF wet-lands have been shown to operate sat-isfactorily at subzero temperatures inWyoming and Montana. Wetlandshave measured pollutant removal effi-ciencies of 24 to 70 percent for phos-phorus and between 31 and 84 per-cent for nitrogen.

Research underway at VirginiaTech (Virginia Polytechnic Instituteand State University) suggests thatcombining engineered wetlands withconventional retention ponds can in-crease phosphorus removal abovethose levels. SF wetlands are beingused to treat dairy feedlot runoff (highBOD and nutrients) in Vermont andare being used to treat airport deicingfacility runoff in Buffalo, New Yorkand Hartford, Connecticut. With theBuffalo project, the runoff has a BODload in excess of 10,000 lbs/day andan effluent discharge permit level of30 mg/L (Whitney, 2008).

POLLUTANT REMOVAL VIA WETLANDS

POND AERATORSAqua Control, Inc.6A Wolfer Industrial Dr.Spring Valley, IL 61362(815) 664-4900www.aquacontrol.comKasco Marine, Inc.800 Deere RoadPrescott, WI 54021(715) 262-4488www.kascomarine.comLAS International, Ltd.216 North 23rd StreetBismarck, ND 58501(701) 222-8331www.lasinternational.comScott Aerator Co. LLC13261 Riley St.Holland, MI 49424(616) 392-8882

www.scottaerator.com

FILTRATION SYSTEMSClear Creek Systems4101 Union Ave.Bakersfield, CA 93305(661) 324-9634www.clearcreeksystems.com

CONTECH ConstructionProducts Inc.9025 Centre Pointe Dr. Ste. 400West Chester, OH 45069(513) 645-7000www.contech-cpi.comFilterra11352 Virginia Precast Rd.Ashland, VA 23005 (866) 349-3458 www.filterra.com

Filtrexx, Inc.35481 Grafton Eastern Rd.Grafton, OH 44044(440) 926-8041www.filtrexx.com

DISINFECTION SYSTEMSAquionics, Inc. 21 Kenton Lands Rd. Erlanger, KY 41018 (859) 341-0710 www.aquionics.comOzone Water Systems5401 South 39th St.Ste. 1Phoenix, Arizona 85040(480) 421-2400www.ozonewatersystems.com

Salcor Engineering447 Ammunition Rd.

Ste. DFallbrook, CA 92028-3292(760) 731-9960Water Tectonics802 134th St. SWSte. 110Everett, WA 98204(425) 742-2062www.watertectonics.com

(Editor’s note: there are liter-ally hundreds of companiesproviding water treatmenttechnologies; this partial listis only provided as a courtesyto BioCycle readers, andshould not be interpreted tobe either complete or an en-dorsement of any of thesecompanies or their products)

STORM WATER TREATMENT SYSTEMS DIRECTORY

ADVANCING COMPOSTING, ORGANICS RECYCLING& RENEWABLE ENERGY

419 State Avenue, Emmaus, PA 18049-3097610-967-4135 • www.biocycle.net

Reprinted With Permission From:April, 2008

BIOCYCLE MAY 2008 39

THE Clean Water Act of 1972 cre-ated the National Pollutant Dis-charge Elimination System(NPDES). Under NPDES, all fa-cilities that discharge pollutantsfrom any point source into U.S.waters are required to obtain a

permit. The U.S. Environmental Protec-tion Agency (EPA), which enforces theClean Water Act (CWA), developed threetypes of NPDES permits for dischargescomprised solely of storm water: individu-al, general and group (or “multisector”)general permits. Most states are delegatedauthority from EPA to regulate storm wa-ter discharges with these types of permits.

Individual storm water permits are verysimilar to standard NPDES permits, set-ting specific numerical effluent limita-tions on conventional, nonconventionaland toxic pollutants, and on hazardoussubstances. General permits are largelyused to control storm water dischargesfrom construction sites disturbing one ormore acres of land (some industrial activi-ties fall under these baseline general per-mits). Multi-sector general permits(MSGP) are aimed at controlling stormwater discharges from similar types of in-dustrial activities, and are grouped alongthe lines of Standard Industrial Classifi-cation (SIC) Codes, in the belief that mostindustrial activities within a particularSIC Code were fundamentally similarwith regard to potential storm waterrunoff contamination potentials.

The challenge for the composting indus-try is that its facilities do not fall neatlyunder one of the regulated industrial cat-egories. None of the specified SIC codesapply specifically to composting facilities,although some composting facilities do usean SIC Code requiring coverage (SIC 2875– Fertilizers, Mixing Only). Others thathave been used include SIC 4953 (Land-fills) for facilities that are located at land-fills, and SIC 2499 (Wood Processing,Misc.). In addition, those composting facil-ities located on farms are exempt from thestorm water permitting requirements ofthe CWA, yet some of those facilities rivalthe more “industrial-scale” facilities foundelsewhere in size, scale and potential wa-ter quality impact.

Storm water discharge general permitsissued to multi-sector SIC code industries(like composters in the SIC 2875 category),while called NPDES permits, do not havethe same effluent limitations on pollutantconcentration, pollutant loading and flowthat is found in traditional end-of-pipeNPDES permits for point sources. Thesegeneral permits are based on periodicmonitoring of key pollutants (correlatedwith the typical storm water contamina-tion profile of that particular SIC Code)and the preparation and implementationof pollution prevention programs.

The monitoring parameters are called“benchmarks,” and the permitted party is

expected to monitor storm water runoff(during a rain event) for those parameterson a periodic basis, either quarterly, semi-annually or annually. If it’s detected thatbenchmarks have been exceeded, the per-mitted party is expected to intensify theirstorm water pollution prevention activi-ties. A Storm Water Pollution PreventionPlan (usually designated as a SWP3 Plan)consists of mapping showing locations ofpollution sources, receiving streams andBest Management Practices (BMPs).

Operational BMPs are basic, everydaypractices and relatively small structuralor equipment requirements that can be ef-fective in preventing pollution, reducingpotential pollutants at the source. Opera-tional practices would include housekeep-ing details like sweeping compost padswith a rotary broom and policies to requireperiodic inspections of storm water man-agement facilities (i.e. looking for trashblockages of drains, etc.). Structural BMPsare measures that control or managestorm water runoff and drainage. Exam-ples include covers and enclosures used toisolate composting and curing pads, andproduct storage areas from rainfall;swales, dikes and berms to divert up-gra-dient runoff from the facility; and stormwater detention basins, vegetative filterstrips, rain gardens (or bioretentionponds) and constructed wetlands to man-age collected runoff.

Part I (February 2008) of this series onstorm water management at compostingfacilities discussed methods for quantify-ing storm water runoff and some of theconstituents in the runoff that are of con-cern in water pollution control. Part II(April 2008) focused on storm water treat-ment options. Part III reviews regulationsin seven states.

STATE REGULATORY STRATEGIESStates vary widely with regard to how

storm water from composting facilities is

Regulationsand permits forstorm waterat compostingfacilitiesinvolve manysite-specificcriteria.

Part III

Craig Coker

WATER QUALITY

STORM WATERMANAGEMENTREGULATIONS

Composting RegulationReview

regulated. Regulators from several stateswere contacted for information about howcompost facility storm water was regulated:

Kansas: Ken Powell, an EnvironmentalScientist with the Kansas Department ofHealth notes, “Compost facilities are splitinto five categories in our regulations:yard waste, manure, livestock (whichmeans dead animals), source-separatedorganic waste and municipal solid waste.Leachate and storm water controls are re-quired at all composting facilities. All ofthe facilities in Kansas are currentlywindrow facilities. Any leachate wouldmix with the storm water. With the excep-tion of MSW composting, all of our facili-ties use either a grass filter strip alone orin combination with a storm water reten-tion structure. Excess water in the controlstructures can be used for watering thewindrows or irrigated on crop fields. We donot currently have any MSW compostingfacilities, but they would be required to beconnected to a municipal sewer system orto haul the leachate to a municipal sewersystem. MSW facilities are also required tobe covered, so they should generate verylittle leachate. In Kansas we have not re-quired NPDES permits since no unfilteredrunoff should leave the facility.

Missouri: Missouri uses the SIC 2875 in-dustrial MSGP to regulate storm waterfrom composting facilities. Missouri usestwo different categories of composting fa-cilities under this SIC Code, one for oper-ations of less than 20 acres composed offeedstocks from agricultural, wood andfood product sources (Permit No. MO-G090000); and the other for operations un-der 20 acres handling any sort of feedstock(Permit No. MO-G920000). Facilities per-mitted under this SIC Code category mustbe nondischarging, except in the event of“emergency discharges during catastroph-ic rain events.” This is defined as the 1 in25 year, 24-hour rainfall, which rangesfrom 5.6 to 7 inches of rain in Missouri.Permits issued under the MO-G920000category require composters to test feed-stocks for heavy metals (not just compost).Benchmark monitoring requirements in-clude BOD, TSS, oil and grease, fecal col-iform, pH, temperature, ammonia-nitro-gen, other forms of nitrogen andphosphorus. Land application of the re-tained storm water is limited to rates ofless than 650,000 gallons per acre peryear. These general permits are tailored toa particular facility’s operation.

North Carolina: Recent regulatory deci-sions in North Carolina have caused con-siderable concern for composters, as thestate’s Department of Environment andNatural Resources (DENR) has decided todeny any future requests for storm waterdischarge permits from composting facili-ties. “Over the past year, we have seen anincreasing number of composting opera-tions seeking NPDES storm water dis-charge permits,” said Bradley Bennett,

Stormwater Permitting Unit Supervisorat North Carolina DENR. “Based on theanalytical data we’ve seen, pollutant lev-els in storm water are more characteristicof wastewater. It is also now clear thatleachate from composting operations is awastewater and poses water quality con-cerns without adequate treatment. We arealso concerned about leachate from fin-ished compost storage piles. Leachate andrunoff from these piles can still introduceconcentrated amounts of oxygen demand,nutrients, solids and other pollutants intosurface waters. We have decided, unlikeother states, that runoff from finishedcompost piles is not storm water, it is aleachate, and should be regulated as awastewater.”

North Carolina DENR’s wastewaterrule requires that all nondischarge alter-natives be fully explored before a wastew-ater discharge permit is issued. Alterna-tives include: eliminate exposure to rainby enclosing the facility; internal recyclingas irrigation water for compost processcontrol; spray application on land; diver-sion to a wastewater treatment plant(WWTP) through the sanitary sewer sys-tem; diversion to a WWTP through a“pump-and-haul;” or treatment on-sitethrough a permitted treatment system(i.e. a “package” WWTP, a constructedwetlands, an evapotranspiration drain-field, etc., or some combination of tech-nologies). Only after demonstrating thatnone of the preceding is feasible, willDENR entertain an application for a dis-charge. Discharges will be subject to wa-ter-quality based effluent limits as needed(i.e., Total Maximum Daily Loads, wholeeffluent toxicity, etc.), and would have ef-fluent limitations much like a regularpoint-source municipal or industrialwastewater discharge.

“Since the policy went into effect, Wal-lace Farms (a multi-feedstock industrialcomposter) has decided to divert to thesanitary sewer system, Brooks (a multi-feedstock industrial composter) is workingon a plan for an on-site treatment system,the City of Durham (a yard waste com-poster) is considering a pump-and-haul toa WWTP and Warren Wilson College (aninstitutional in-vessel composter) is con-sidering an exclusion from coverage basedon being in-vessel,” said Frank Franciosiof the Carolinas Composting Council. Dis-cussions are underway between the Coun-cil and DENR about the nature and typesof cost-effective on-site treatment systemsthat will meet state water quality permit-ting requirements.

Oregon: One of the more progressive ap-proaches to managing storm water may befound in Oregon. “We found that regulat-ing storm water from composting facilitiesunder the Industrial General Storm WaterPermits didn’t adequately cover all on-siteactivities of composters,” says JenineCamilleri, with the Water Quality Divi-

40 BIOCYCLE MAY 2008

Oregon DEQdeveloped a specificpermit forcomposters focusedon the use of BMPsto treat storm water.

sion of Oregon Department of Environ-mental Quality (DEQ). “So we developed aspecific storm water permit for com-posters, known as the 1200-CP GeneralStorm Water Permit.” This new permit isfocused on the use of BMPs to treat stormwater from compost. Quarterly monitoringwill be required of BOD and phosphorus inaddition to the standard industrial stormwater monitoring parameters of copper,lead, zinc, pH, suspended solids and oiland grease. This permit also requires: pub-lic notice and comment on the applicationand on the storm water management plan;requires runoff meet in-stream waterquality standards; and composting facili-ties obtain an individual NPDES permit ifthey have failed after the fourth year ofpermit coverage to consistently meet themonitoring benchmarks. (Table 1 lists pro-posed benchmarks). Exemptions from thisrule will be limited to home composting,agricultural composting of agriculturalwaste and institutional composting of self-generated wastes (and on-site use of theresulting compost only).

Under new composting rules being pre-pared by Oregon DEQ Land Quality(which include the new storm water per-mit rules), leachate will have to be segre-gated from storm water and handled sep-arately. If leachate is commingled withstorm water, the facility is not eligible forthe 1200-CP permit. “We’re considering ajoint permitting process for both permits(Solid Waste and Water Quality) with oneapplication,” notes Camilleri. The newrules (currently in draft form) will requirethat leachate production be minimized,that it be collected and directed to an im-permeable containment structure, thattanks used to store leachate have sec-ondary containment and that it be eitherdirected to a treatment plant, or if treatedon-site, then discharged under a NPDESpermit with effluent limitations.

Virginia: Solid waste composting facili-ties (which includes everything from yardtrimmings to commingled municipal solidwaste) are required to capture, containand prevent discharge of runoff from the 1-hour, 10-year storm. Runoff above thatlevel is regulated under the Industrial Ac-tivity General Permit for SIC 2875 (Fertil-izers, mixing only). Benchmark monitor-ing parameters are: Total Nitrogen (2.2mg/l), Total Recoverable Iron (1.0 mg/l),Total Recoverable Zinc (120 µg/l) and To-tal Phosphorus (2 mg/l). Facilities are alsorequired to conduct visual monitoring(recording their observations), annualmonitoring and preparation and adoptionof a SWP3 Plan.

Washington: Composting facilities inWashington are required to separateleachate from storm water; storm waterrunning off a compost pad is consideredleachate. “Compost facilities here usuallyrequire an Industrial Storm Water NPDESpermit,” said Chery Sullivan, a composting

specialist with the Washington Depart-ment of Ecology. “Washington has been del-egated to run EPA’s NPDES permit pro-gram and is authorized to administer theIndustrial Storm Water NPDES in lieu ofEPA’s Multi-Sector permit.” She also notedthat most facilities manage storm water on-site through detention and infiltration ordischarge storm water offsite under a per-mit. “If they manage storm water onsite,they may not need a permit,” Sullivan said.“Depth to groundwater, runoff volume andrisk of contamination all play a role in thedetermination of needing a permit for thosewho retain storm water on site.”

Wisconsin: In Wisconsin, leachate is reg-ulated and is required to be segregatedfrom storm water. “Leachate treatment isrequired to a varying extent depending onthe facility,” said Gretchen Wheat, an en-gineer with the Wisconsin Department ofNatural Resources (WIDNR). “It dependson waste types, facility size, location fac-tors, etc. Berms, ditches or other meansmust be used to prevent run-on of noncon-tact storm water. Leachate includes waterthat comes in contact with materials in thecomposting process.”

Brad Wolbert, a hydrogeologist withWIDNR’s, Bureau of Waste and MaterialsManagement, has recently taken the leadon solid waste composting. Wolbert ex-plained, “Solid waste composting facilitieswith feedstocks limited to certain sourcesegregated materials are regulated by s.NR 502.12. The rule is mainly for yard ma-terials and vegetable food waste compostedby low tech methods. Composting facilitiesthat are small or have lower nutrient ma-terials can generally discharge leachate orrun off to a vegetated filter strip area. Fa-cilities that are large or have higher nutri-ents need to capture leachate, and the rulespecifies two management options: recircu-late into the composting process, or dis-charge to permitted wastewater treatmentfacility. Potentially leachate could be dis-charged to a wastewater treatment strip,but a WPDES Permit may be required, and

BIOCYCLE MAY 2008 41

Table 1. Oregon’s proposed storm water monitoring benchmarks for compostingoperations

Parameter Benchmark

Total copper 0.1 mg/l Total lead 0.4 mg/l Total zinc 0.6 mg/l pH 5.5 – 9.0 SU Total suspended solids 130 mg/l Total oil & grease 10 mg/l BOD5 30 mg/l Total phosphorous 2 mg/l Floating solids (associated with composting activities) No visible discharge Oil & grease sheen No visible sheen

1Applies only to facilities not discharging to the Columbia Slough Watershed; those facilities also have anE. Coli monitoring benchmark and different benchmark concentrations than those above.

an applicant would need to demonstratethe effectiveness of any proposed treat-ment option. Composting of other feed-stocks is regulated by s. NR 502.08, Wis-consin Administrative Code, a moregenerally written rule that allows flexibili-ty to address processing of various solidwastes by any method shown to be envi-ronmentally sound.”

Wolbert went on to note, “Storm waterfrom a compost pad is considered leachate,and a curing pad is considered a compostpad. So, runoff from curing pads is regu-lated under the same authority, but differ-ent (less) treatment might be needed.Product storage piles may also be regulat-ed under the same authority, but again,required treatment would be less.”

Wheat added, “A starting place to guidecompost leachate treatment design mightbe Natural Resource Conservation Service(NRCS) Standards 635 Wastewater Treat-ment Strip, 393 Filter Strip and 590 Nutri-ent Management. Treatment strip designcommonly includes capture of more concen-trated initial flow. However, manure hasmuch higher nutrients than expected incompost leachate, so I’m not suggesting todirectly use NRCS Standards.” �

Craig Coker is a Contributing Editor to Bio-Cycle and a Principal in the firm of CokerComposting & Consulting in Roanoke, Vir-ginia (www.cokercompost.com). He can bereached at (540) 904-2698 or by email atcraigcoker@cox.net.

42 BIOCYCLE MAY 2008

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