United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati, OH 45268 Research and Development EPA/600/SR-94/051 May 1994 EPA Project Summary Potential Groundwater Contamination from Intentional and Nonintentional Stormwater Infiltration Robert Pitt, Shirley Clark, and Keith Farmer The research summarized here was conducted during the first year of a 3- yr cooperative agreement to identify and control stormwater toxicants, es- pecially those adversely affecting groundwater. The purpose of this re- search effort was to review the ground- water contamination literature as it relates to stormwater. Potential prob- lem pollutants were identified, based on their mobility through the unsatur- ated soil zone above groundwater, their abundance in stormwater, and their treatability before discharge. This in- formation was used with earlier EPA research results to identify the pos- sible sources of these potential prob- lem pollutants. Recommendations were also made for stormwater infiltration guidelines in different areas and moni- toring that should be conducted to evaluate a specific stormwater for its potential to contaminate groundwater. This Project Summary was developed by EPA's Risk Reduction Engineering Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction Before urbanization, groundwater was recharged by precipitation infiltrating through pervious surfaces, including grass- lands and woods. This infiltrating water was relatively uncontaminated. Urbaniza- tion, however, reduced the permeable soil surface area through which recharge by infiltration could occur. This resulted in much less groundwater recharge and greatly increased surface runoff. In addi- tion, the waters available for recharge gen- erally carried increased quantities of pollutants. With urbanization, waters hav- ing elevated contaminant concentrations also recharge groundwater, including ef- fluent from domestic septic tanks, waste- water from percolation basins and industrial waste injection wells, infiltrating stormwater, and infiltrating water from ag- ricultural irrigation. This report addresses potential groundwater problems associated with stormwater toxicants and describes how conventional stormwater control prac- tices can reduce these problems. Sources of Pollutants High bacteria populations have been found in sheetflow samples from sidewalks, roads, and some bare ground (collected from locations where dogs would most likely be "walked"). Tables 1 and 2 sum- marize toxicant concentrations and likely sources or locations having some of the highest concentrations found during an earlier phase of this EPA-funded research. The detection frequencies for the heavy metals are all close to 100% for all source areas, and the detection frequencies for the organics listed on these tables ranged from about 10% to 25%. Vehicle service areas had the greatest abundance of ob- served organics. ------- Table 1. Concentrations of Heavy Metals in Observed Areas Toxicant Highest Median Highest Observed Cadmium Chromium Copper Lead Nickel Zinc Vehicle service area runoff Landscaped area runoff Urban receiving water CSO Parking area runoff Roof runoff 8 100 160 75 40 100 Street runoff Roof runoff Street runoff Storage area runoff Landscaped area runoff Roof runoff 220 510 1250 330 130 1580 Table 2. Maximum Concentrations of Toxic Organics from Observed Sources Toxicant Benzo (a) anthracene Benzo (b) fluoranthene Benzo (k) fluoranthene Benzo (a) pyrene Fluorantnene Naphthalene Phenanthrene Pyrene Chlordane Butyl benzyl phthalate Bis (2-chloroethyl) ether Bis (2-chloroisopropyl) ether 1 ,3-Dichlorobenzene Maximum, W/L 60 226 221 300 128 296 69 102 2.2 128 204 217 120 Detection Frequency, % 12 17 17 17 23 13 10 19 13 12 14 14 23 Significant Sources Gasoline, wood preservative Gasoline, motor oils Gasoline, bitumen, oils Asphalt, gasoline, oils Oils, gasoline, wood preservative Coal tar, gasoline, insecticides Oils, gasoline, coal tar Oils, gasoline, bitumen, coal tar, wood preservative Insecticide Plasticizer Fumigant, solvents, insecticides, paints, lacquers, varnishes Pesticide manufacturing Pesticide manufacturing Stormwater Constituents Having High Potential to Contaminate Groundwater Nutrients Nitrates are one of the most frequently encountered contaminants in groundwa- ter. Phosphorus contamination of ground- water has not been as widespread, or as severe, as that of nitrogen compounds. Whenever nitrogen-containing compounds come into contact with soil, a potential exists for nitrate leaching into groundwa- ter, especially in rapid-infiltration waste- water basins, stormwater infiltration devices, and agricultural areas. Nitrate has leached from fertilizers and affected groundwaters under various turf grasses in urban areas, including golf courses, parks, and home lawns. Significant leach- ing of nitrates occurs during the cool, wet seasons. Cool temperatures reduce deni- trification and ammonia volatilization and limit microbial nitrogen immobilization and plant uptake. The use of slow-release fer- tilizers (including composted organic mulches, urea formaldehyde (UF), meth- ylene urea, isobutylidene diurea (IBDU), and sulfur-coated urea) is recommended in areas having potential groundwater ni- trate problems. Residual concentrations of nitrate in soil vary greatly and depend on the soil tex- ture, mineralization, rainfall and irrigation patterns, organic matter content, crop yield, nitrogen fertilizer/sludge application rate, denitrification, and soil compaction. Nitrate is highly soluble (>1 kg/L) and will stay in solution in the percolation water. If it leaves the root zone without being taken-up by plants, it will readily reach the groundwa- ter. Pesticides Urban pesticide contamination of groundwater can result from municipal and homeowner use for pest control and the subsequent collection of the pesticide in stormwater runoff. Pesticides that have been found in urban groundwaters include: 2,4-D, 2,4,5-T, atrazine, chlordane, diazinon, ethion, malathion, methyl trithion, silvex, and simazine. Heavy repetitive use of mobile pesticides (those that are not likely to be retained by various processes in the soil before they reach the ground- water, such as 2,4-D, acenaphthylene, alachlor, atrazine, cyanazine, dacthal, diazinon, dicamba, and malathion) on irri- gated and sandy soils will likely contami- nate groundwater. Fungicides and nematocides must be mobile to reach the target pest, and hence, they generally have the highest groundwater contamination potential. Pesticide leaching depends on patterns of use, soil texture, total organic carbon content of the soil, pesticide per- sistence, and depth to the water table. The greatest pesticide mobility occurs in areas with coarse-grained or sandy soils without a hardpan layer, and with soils that have low clay and organic matter content and high permeability. Structural voids, generally found in the surface layer of finer-textured soils rich in clay, can trans- mit pesticides rapidly when the voids are filled with water and the adsorbing sur- faces of the soil matrix are bypassed. In general, pesticides with low water solubili- ties, high octanol-water partitioning coeffi- cients, and high carbon partitioning coefficients are less mobile. The slower moving pesticides that may better sorb to soils have been recommended for use in areas of groundwater contamination con- cern. These include the fungicides iprodione and triadimefon, the insecticides isofenphos and chlorpyrifos, and the her- bicide glyphosate. Pesticides decompose in soil and wa- ter, but the total decomposition time can range from days to years. Literature half- lives for pesticides generally apply to sur- face soils and do not account for the reduced microbial activity found deep in the vadose zone. Pesticides with a 30- day half life can show considerable leach- ing. An order-of-magnitude difference in half-life results in a five- to ten-fold differ- ence in percolation loss. Organophosphate pesticides are less persistent than orga- nochlorine pesticides, but they also are not strongly adsorbed by the sediment and are likely to leach into the vadose zone and the groundwater. Other Organics The most commonly occurring organic compounds found in urban groundwaters include phthalate esters (especially bis(2- ethylhexyl)phthalate) and phenolic com- pounds. Other, more rarely found, organics include the volatiles: benzene, chloroform, methylene chloride, trichloroethylene, tetrachloroethylene, toluene, and xylene. Polycyclic aromatic hydrocarbons (PAHs) (especially benzo(a)anthracene, chrysene, anthracene, and benzo(b)fluoroanthenene) have also been found in groundwaters near industrial sites. Groundwater contamination from organ- ics, like that from other pollutants, occurs ------- more readily in areas with sandy soils and where the water table is near the land surface. Organics can be removed from the soil and recharge water by volatiliza- tion, sorption, and degradation. Volatiliza- tion can significantly reduce the concentrations of the most volatile com- pounds in groundwater, but the rate of gas transfer from the soil to the air is usually limited by the presence of soil water. Hydrophobic sorption onto soil or- ganic matter limits the mobility of less soluble base/neutral and acid extractable compounds through organic soils and the vadose zone. Sorption is not always a permanent removal mechanism, however. Organic resolubilization can occur during wet periods following dry periods. Many organics can be degraded by microorgan- isms, at least partially, but others cannot. Temperature, pH, moisture content, ion exchange capacity of the soil, and air avail- ability may limit the microbial degradation potential for even the most degradable organic compound. Microorganisms Viruses have been detected in ground- water where stormwater recharge basins were located short distances above the aquifer. Enteric viruses are more resistant to environmental factors than are enteric bacteria, and they exhibit longer survival times in natural waters. They can occur in potable and marine waters in the absence of fecal coliforms. Enteroviruses are also more resistant to commonly used disin- fectants than are indicator bacteria (such as fecal coliforms), and they can occur in groundwater in the absence of indicator bacteria. The factors that affect the survival of enteric bacteria and viruses in the soil include pH, antagonism from soil microf- lora, moisture content, temperature, sun- light, and organic matter. The two most important attributes of viruses that permit their long-term survival in the environment are their structure and very small size. These characteristics permit virus occlu- sion and protection within colloid-size par- ticles. Viral adsorption is promoted by increasing cation concentration, decreas- ing pH, and decreasing soluble organics. Since the movement of viruses through soil to groundwater occurs in the liquid phase and involves water movement and associated suspended virus particles, the distribution of viruses between the adsorbed and liquid phases determines the viral mass available for movement. Once the virus reaches the groundwater, it can travel laterally through the aquifer until it is either adsorbed or inactivated. The major bacterial removal mecha- nisms in soil are straining at the soil sur- face and at intergrain contacts, sedimentation, sorption by soil particles, and inactivation. Because their size is larger than viruses, most bacteria are re- tained near the soil surface because of this straining effect. In general, enteric bacteria survive in soil between 2 and 3 mo, although survival times up to 5 yr have been documented. Metals From a groundwater pollution standpoint, the metals in stormwater presenting the most environmental concern are alumi- num, arsenic, cadmium, chromium, cop- per, iron, lead, mercury, nickel, and zinc. The majority of these metals (with the common exception of zinc) are, however, mostly associated with the particulate frac- tions and can be mostly removed by ei- ther sedimentation or filtration processes. In general, studies of recharge basins receiving large metal loads found that most of the heavy metals are removed either in the basin sediment or in the vadose zone. Dissolved metal ions are removed from stormwater during infiltration mostly by adsorption onto the near-surface particles in the vadose zone, and the particulate metals are filtered out at the soil surface. Studies at recharge basins found that lead, zinc, cadmium, and copper accumulated at the soil surface with little downward movement over many years. At a com- mercial site, however, nickel, chromium, and zinc concentrations have exceeded regulatory limits in the soils below a re- charge area. Allowing percolation ponds to go dry between storms can be counter- productive to the removal of lead from the water during recharge. Apparently, the adsorption bonds between the sediments and the metals can be weakened during the drying period. Similarities in water quality between run- off water and groundwater have shown that there is significant downward move- ment of copper and iron in sandy and loamy soils. Arsenic, nickel, and lead, how- ever, did not significantly move downward through the soil to the groundwater. The exception to this was some downward movement of lead with the percolation water in sandy soils beneath stormwater recharge basins. Zinc, which is more soluble than iron, has been found in higher concentrations in groundwater than iron. The order of attenuation in the vadose zone from infiltrating stormwater is: zinc (most mobile) > lead > cadmium > man- ganese > copper > iron > chromium > nickel > aluminum (least mobile). Salts Salt applications for winter traffic safety is a common practice in many northern areas, and the sodium and chloride, which are collected in the snowmelt, travel down through the vadose zone to the ground- water with little attenuation. Soil is not very effective at removing salts. Salts that are still in the percolation water after it travels through the vadose zone will con- taminate the groundwater. Infiltrating stormwater has increased sodium and chloride concentrations above background concentrations. Fertilizer and pesticide salts also accumulate in urban areas and can leach through the soil to the ground- water. Studies of depth of pollutant penetra- tion in soil have shown that sulfate and potassium concentrations decrease with depth, whereas sodium, calcium, bicar- bonate, and chloride concentrations in- crease with depth. Once contamination with salts begins, the movement of salts into the groundwater can be rapid. The salt concentration may not lessen until the source of the salts is removed. Treatment of Stormwater Table 3 summarizes the filterable frac- tion of toxicants found in runoff sheet flows from many urban areas found during an earlier phase of this EPA-funded research. Pollutants that are mostly in filterable forms have a greater potential of affecting groundwater and are more difficult to con- trol with the use of conventional stormwater control practices which mostly rely on sedi- mentation and filtration principles. Luckily, most of the toxic organics and metals are associated with the nonfilterable (sus- pended solids) fraction of the wastewa- ters during wet weather. Possible exceptions include zinc, fluoranthene, pyrene, and 1,3-dichlorobenzene, which may be mostly found in the filtered sample portions. Pollutants in dry-weather storm drainage flows, however, tend to be much more associated with filtered sample frac- tions and would not be as readily con- trolled with the use of sedimentation. Sedimentation is the most common fate and control mechanism for particulate-re- lated pollutants. This would be common for most stormwater pollutants, as noted above. Particulate removal can occur in many conventional stormwater control pro- cesses, including catchbasins, screens, drainage systems, and detention ponds. Sorption of pollutants onto solids and metal precipitation increases the sedimentation potential of these pollutants and also en- courages more efficient bonding of the pollutants in soils to prevent their leaching ------- Table 3. Reported Filterable Fractions of Stormwater Toxicants from Source Areas Constituent Cadmium Chromium Copper Iron Lead Nickel Zinc Benzo (a) anthracene Fluoranthene Naphthalene Phenanthrene Pyrene Chlordane Butyl benzyl phthalate Bis (2-chloroethyl) ether Bis (2-chlrorisopropyl) ether 1 ,3-Dichlorobenzene Filterable Fraction (%) 20 to 50 <10 <20 Small amount <20 Small amount >50 None found in 65 25 None found in 95 None found in Irregular Irregular None found in 75 filtered fraction filtered fraction filtered fraction filtered fraction to groundwaters. Detention ponds are probably the most common management practice for the control of stormwater run- off. If properly designed, constructed, and maintained, wet detention ponds can be very effective in controlling a wide range of pollutants. The monitored performance of wet detention ponds indicates more than 90% removal for suspended solids, 70% for BOD5 and COD, about 60% to 70% for nutrients, and about 60% to 95% for heavy metals. Catchbasins are very small sedi- mentation devices. Adequate cleaning can help reduce the total solids and lead ur- ban runoff yields by between 10% and 25%, and COD, total Kjeldahl nitrogen, total phosphorus, and zinc by between 5% and 10%. Other important fate mecha- nisms available in wet detention ponds, but which are probably not important in small enclosed sump devices such as catchbasins, include volatilization and pho- tolysis. Biodegradation, biotransformation, and bioaccumulation (into plants and ani- mals) may also occur in larger and open ponds. Upland infiltration devices (such as infil- tration trenches, porous pavements, per- colation ponds, and grass roadside drainage swales) are located at urban source areas. Infiltration (percolation) ponds are usually located at stormwater outfalls or at large paved areas. These basins, along with perforated storm sew- ers, can infiltrate flows and pollutants from all upland sources combined. Infiltration devices can safely deliver large fractions of the surface flows to groundwater, if carefully designed and located. Local con- ditions that can make stormwater infiltra- tion inappropriate include steep slopes, slowly percolating soils, shallow ground- water, and nearby groundwater uses. Grass filter strips may be quite effective in removing particulate pollutants from over- land flows. The filtering effects of grasses, along with increased infiltration/recharge, reduce the particulate sediment load from urban landscaped areas. Grass swales are another type of infiltration device and can be used in place of curb and gutter drainages in most land uses, except pos- sibly strip commercial and high density residential areas. Grass swales allow the recharge of significant amounts of surface flows. Swales can also reduce pollutant concentrations because of filtration. Soluble and particulate heavy metal (cop- per, lead, zinc, and cadmium) concentra- tions can be reduced by at least 50%, COD, nitrate nitrogen, and ammonia nitro- gen concentrations can be reduced by about 25%, but only inconsistent concen- tration reductions can be expected for or- ganic nitrogen, phosphorus, and bacteria. Sorption of pollutants to soils is prob- ably the most significant fate mechanism of toxicants in biofiltration devices. Many of the devices also use sedimentation and filtration to remove the particulate forms of the pollutants from the water. Incorpo- ration of the pollutants onto soil with sub- sequent biodegradation and minimal leaching to the groundwater is desired. Volatilization, photolysis, biotransformation, and bioconcentration may also be signifi- cant in grass filter strips and grass swales. Underground seepage drains and porous pavements offer little biological activity to reduce toxicants. Results and Conclusions This entire research project will provide guidance on critical source area treatment, especially for the protection of groundwa- ter quality. Much of the information will also be useful for analyzing stormwater problems and needed controls for surface water discharges. Table 4 is a summary of the pollutants found in stormwater that may cause groundwater contamination problems for various reasons. This table does not con- sider the risk associated with using ground- water contaminated with these pollutants. Causes of concern include high mobility (low sorption potential) in the vadose zone, high abundance (high concentrations and high detection frequencies) in stormwater, and high soluble fractions (small fraction associated with particulates that would have little removal potential using conven- tional stormwater sedimentation controls) in the stormwater. The contamination po- tential is the lowest rating of the influenc- ing factors. As an example, when no pretreatment is used before percolation through surface soils, the mobility and abundance criteria are most important. When a compound is mobile but in low abundance (such as for volatile organic compounds, VOCs), then the groundwa- ter contamination potential would be low. When the compound is mobile, however, and also in high abundance (such as for sodium chloride, in certain conditions), then the groundwater contamination potential would be high. When sedimentation pre- treatment is to be used before infiltration, then some of the pollutants will likely be removed before infiltration. In this case, all three influencing factors (pollutant mo- bility, pollutant abundance in stormwater, and fraction of the pollutant associated with the filtered sample fraction) would be considered. As an example, chlordane would have a low contamination potential with sedimentation pretreatment, whereas it would have a moderate contamination potential when no pretreatment is used. In addition, when subsurface infiltration/injec- tion is used instead of surface percola- tion, the compounds would most likely be more mobile, making the abundance cri- teria the most important, with some re- gard given to the filterable fraction information for operational considerations. This table is only appropriate for initial estimates of contamination potential be- cause of the simplifying assumptions made, such as the worst case mobility conditions assumed (for sandy soils hav- ing low organic content). When the soil is clayey and has a high organic content, then most of the organic compounds would be less mobile than that shown on this table. The abundance and filterable frac- tion information is generally applicable for warm weather stormwater runoff in resi- dential and commercial areas. The pollut- ant concentrations and detection ------- frequencies, however, would be greater for critical source areas (especially ve- hicle service areas) and critical land uses (especially manufacturing industrial areas). The stormwater pollutants of most con- cern (those that may have the greatest adverse impacts on groundwaters) include: • Nutrients: nitrate has a low to moder- ate potential for contaminating ground- water when both surface percolation and subsurface infiltration/injection are used because of its relatively low con- centrations in most stormwaters. When the stormwater nitrate concen- tration is high, then the groundwater contamination potential would likely also be high. • Pesticides: lindane and chlordane have moderate potentials for contami- nating groundwater when surface per- colation (with no pretreatment) or when subsurface injection (with mini- mal pretreatment) are used. The groundwater contamination potentials for both of these compounds would very likely be substantially reduced with adequate sedimentation pretreat- ment. • Other organics: 1,3-dichlorobenzene may have a high potential for con- taminating groundwater when subsur- face infiltration/injection (with minimal pretreatment) is used. It would, how- ever, probably have a lower ground- water contamination potential for most surface percolation practices because of its relatively strong sorption to va- dose zone soils. Both pyrene and fluoranthene would also very likely have high groundwater contamination potentials for subsurface infiltration/ injection practices, but lower contami- nation potentials for surface percola- tion practices because of their more limited mobility through the unsatur- ated zone (vadose zone). Others (in- cluding benzo(a)anthracene, bis (2-ethylhexyl) phthalate, pentachlo- rophenol, and phenanthrene) may also have moderate groundwater con- tamination potentials when surface percolation with no pretreatment, or subsurface injection/infiltration, is used. These compounds would have low groundwater contamination poten- tials when surface infiltration is used with sedimentation pretreatment. VOCs may also have high groundwa- ter contamination potentials if present in the stormwater (which is possible for some industrial and commercial facilities and vehicle service estab- lishments). • Pathogens: enteroviruses very likely have high potentials for contaminat- ing groundwater when any percola- tion or subsurface infiltration/injection practice is used, depending on their presence in stormwater (especially if contaminated with sanitary sewage). Other pathogens, including Shigella, Pseudomonas aeruginosa, and vari- ous protozoa, would also have high groundwater contamination potentials when subsurface infiltration/injection practices are used without disinfec- tion. When disinfection (especially by chlorine or ozone) is used, then disin- fection by-products (such as trihalomethanes or ozonated bro- mides) would have high groundwater contamination potentials. • Heavy Metals: nickel and zinc possi- bly have high potentials for contami- nating groundwater when subsurface infiltration/injection is used. Chromium and lead would have moderate groundwater contamination potentials for subsurface infiltration/injection practices. All metals would possibly have low groundwater contamination potentials when surface infiltration is used with sedimentation pretreatment. • Salts: chloride would very likely have a high potential for contaminating groundwater in northern areas where road salts are used for traffic safety, irrespective of the pretreatment, infil- tration, or percolation practices used. Pesticides have been mostly found in urban runoff from residential areas, espe- cially in dry weather flows associated with landscaping irrigation runoff. The other or- ganics, especially the volatiles, are mostly found in industrial areas. The phthalates are found in all areas. The PAHs are also found in runoff from all areas, but they are in higher concentrations and occur more frequently in industrial areas. Pathogens are most likely associated with sanitary sewage contamination of storm drainage systems, but several bacterial pathogens are commonly found in surface runoff in residential areas. Zinc is mostly found in roof runoff and other areas where galva- nized metal comes into contact with rain- water. Salts are at their greatest concentrations in snowmelt and early spring runoff in northern areas. The control of these compounds re- quires various approaches, including source area controls, end-of-pipe controls, and pollution prevention. All dry weather flows should be diverted from infiltration devices because of their potentially high concentrations of soluble heavy metals, pesticides, and pathogens. Similarly, all runoff from manufacturing industrial areas should also be diverted from infiltration devices because of their relatively high concentrations of soluble toxicants. Com- bined sewer overflows should also be di- verted because of sewage contamination. In areas of snow and ice control, winter snowmelt and runoff and early spring run- off should also be diverted from infiltration devices. All other runoff should include pretreat- ment using sedimentation processes be- fore infiltration, to both minimize groundwater contamination and to prolong the life of the infiltration device (if needed). This pretreatment can take the form of grass filters, sediment sumps, wet deten- tion ponds, etc., depending on the runoff volume to be treated, treatment flow rate, and other site specific factors. Pollution prevention can also play an important role in minimizing groundwater contamination problems, including reducing the use of galvanized metals, pesticides, and fertiliz- ers in critical areas. The use of special- ized treatment devices, such as those being developed and tested during this research, can also play an important role in treating runoff from critical source ar- eas before these more contaminated flows commingle with cleaner runoff from other areas. Sophisticated treatment schemes, especially the use of chemical processes or disinfection, may not be warranted, ex- cept in special cases, especially when the potential of forming harmful treatment by- products (such as THMs and soluble alu- minum) is considered. The use of surface percolation devices (such as grass swales and percolation ponds) that have a substantial depth of underlying soils above the groundwater is preferable to the use of subsurface infil- tration devices (such as dry wells, trenches or seepage drains, and especially injec- tion wells), unless the runoff water is known to be relatively free of pollutants. Surface devices are able to take greater advan- tage of natural soil pollutant removal pro- cesses. Unless all percolation devices are carefully designed and maintained, how- ever, they may not function properly and may lead to premature hydraulic failure or contamination of the groundwater. Recommendations With a reasonable degree of site-spe- cific design considerations to compensate for soil characteristics, infiltration may be ------- Table 4. Potential of Stormwater Pollutants to Contaminate Groundwater Compounds Nutrients Pesticides Other organics Pathogens Heavy metals Salts nitrates 2,4-D Y-BHC (lindane) malathion atrazine chlordane diazinon VOCs 1 ,3-dichloro- benzene anthracene benzo(a) anthracene bis (2-ethylhexyl) phthalate butyl benzyl phthalate fluoranthene fluorene naphthalene pentachlorophenol phenanthrene pyrene enteroviruses Shigella Pseudomonas aeruginosa protozoa nickel cadmium chromium lead zinc chloride Mobility (sandy/low organic soils) mobile mobile intermediate mobile mobile intermediate mobile mobile low intermediate intermediate intermediate low intermediate intermediate low/inter. intermediate intermediate intermediate mobile low/inter. low/inter. low/inter. low low inter. /very low very low low/very low mobile Abundance in Stormwater low/moderate low moderate low low moderate low low high low moderate moderate low/moderate high low low moderate moderate high likely present likely present very high likely present high low moderate moderate high seasonally high Fraction Filterable high likely low likely low likely low likely low very low likely low very high high moderate very low likely low moderate high likely low moderate likely low very low high high moderate moderate moderate low moderate very low very low high high Surface Infill, and No Pretreatment low/moderate low moderate low low moderate low low low low moderate moderate low moderate low low moderate moderate moderate high low/moderate low/moderate low/moderate low low low/moderate low low high Contamination Potential Surface Infill, with Sub-surface Inj. with Sedimentation Minimal Pretreatment low/moderate low low low low low low low low low low low low moderate low low low low moderate high low/moderate low/moderate low/moderate low low low low low high low/moderate low moderate low low moderate low low high low moderate moderate low/moderate high low low moderate moderate high high high high high high low moderate moderate high high very effective in controlling both urban run- off quality and quantity problems. This strategy encourages infiltration of urban runoff to replace the natural infiltration ca- pacity lost through urbanization and to use the natural filtering and sorption ca- pacity of soils to remove pollutants; how- ever, the potential for some types of urban runoff to contaminate groundwater through infiltration requires some restrictions. Infil- tration of urban runoff having potentially high concentrations of pollutants that may pollute groundwater requires adequate pre- treatment or the diversion of these waters away from infiltration devices. The follow- ing general guidelines for the infiltration of Stormwater and other storm drainage ef- fluent are recommended in the absence of comprehensive site-specific evaluations: Dry weather storm drainage effluent should be diverted from infiltration devices because of their probable high concentrations of soluble heavy met- als, pesticides, and pathogenic mi- croorganisms. Combined sewage overflows should be diverted from infiltration devices because of their poor water quality, especially their high pathogenic mi- croorganism concentrations and high clogging potential. Snowmelt runoff should be diverted from infiltration devices because of its potential for having high concen- trations of soluble salts. Runoff from manufacturing industrial areas should be diverted from infiltra- tion devices because of its potential for having high concentrations of soluble toxicants. Construction site runoff must be di- verted from Stormwater infiltration de- vices (especially subsurface devices) because of its high suspended solids concentrations, which would quickly clog infiltration devices. Runoff from other critical source ar- eas, such as vehicle service facilities and large parking areas, should at least receive adequate pretreatment to eliminate their groundwater con- tamination potential before infiltration. Runoff from residential areas (the larg- est component of urban runoff in most cities) is generally the least polluted urban runoff flow and should be con- sidered for infiltration. Very little treat- ------- ment of residential area stormwater runoff should be needed before infil- tration, especially if surface infiltration is through the use of grass swales. When subsurface infiltration (seepage drains, infiltration trenches, dry wells, etc.) is used, then some pretreatment may be needed, such as by using grass filter strips, or other surface fil- tration devices. Recommended Stormwater Quality Monitoring to Evaluate Potential Groundwater Contamination Most past stormwater quality monitor- ing efforts have not adequately evaluated stormwater's potential for contaminating groundwater. The following list shows the stormwater contaminants that are recom- mended for monitoring when stormwater contamination potential needs to be con- sidered, or when infiltration devices are to be used. Other analyses are appropriate for additional monitoring objectives (such as evaluating surface water problems). In addition, all phases of urban runoff should be sampled, including stormwater runoff, dry-weather flows, and snowmelts. • Urban runoff contaminates with the potential to adversely affect ground- water: - Nutrients (especially nitrates) - Salts (especially chloride) - VOCs (if expected in the runoff, such as runoff from manufacturing in- dustrial or vehicle service areas, could screen for VOCs with purgable or- ganic carbon analyses) - Pathogens (especially enteroviruses, if possible, along with other patho- gens such as Pseudomonas aeruginosa, Shigella, and pathogenic protozoa) - Bromide and total organic carbon (to estimate disinfection by-product generation potential, if disinfection by either chlorination or ozone is being considered) - Pesticides, in both filterable and to- tal sample components (especially lin- dane and chlordane) - Other organics, in both filterable and total sample components (especially 1,3 dichlorobenzene, pyrene, fluoranthene, benzo(a)anthracene, bis (2-ethylhexyl) phthalate, pentachlo- rophenol, and phenanthrene) - Heavy metals, in both filterable and total sample components (especially chromium, lead, nickel, and zinc) Urban runoff compounds with the po- tential to adversely affect infiltration and injection operations: - Sodium, calcium, and magnesium (to calculate the sodium adsorption ratio to predict clogging of clay soils) - Suspended solids (to determine the need for sedimentation pretreatment to prevent clogging) ------- Robert Pitt, Shirley Clark and Keith Farmer are with the Department of Civil and Environmental Engineering, the University of Alabama at Birmingham, Birmingham, AL 35294 Richard Field is the EPA Project Officer (see below). The complete report, entitled "Potential Groundwater Contamination from Intentional and Nonintentional Stormwater Infiltration," (Order No. PB94- 165354AS; Cost: $27.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Risk Reduction Engineering Laboratory U.S. Environmental Protection Agency Edison, NJ 08837-3679 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-94/051 ------- |