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GROUNDWATER CONTAMINATION FROM STORMWATER INFILTRATION Robert Pitt, Shirley Clark and Keith Parmer Department of Civil and Environmental Engineering, The University of Alabama at Birmingham University
GROUNDWATER CONTAMINATION FROM STORMWATER INFILTRATION Robert Pitt, Shirley Clark and Keith Parmer Department of Civil and Environmental Engineering, The University of Alabama at Birmingham University Station, Birmingham, AL (205) INlRODUCTlON Richard Field and Thomas P. O'Connor Storm and Sewer Pollution Control Program, U.S. Environmental Protection Agency 2890 Woodbridge Avenue, Edison, NJ (908) The research summarized here was conducted during the first year of a 3-yr cooperative agreement (CR819573) to identify and control stormwater toxicants, especially those adversely affecting groundwater. The purpose of this research effort was to review the groundwater contamination literature as it relates to stormwater. Prior to urbanization groundwater is recharged by rainfall-runoff and snowmelt infiltrating through pervious surfaces including grasslands and woods. This infiltrating water is relatively uncontaminated. Urbanization, however, reduces the permeable soil surface area through which recharge by infiltration occurs. This results in much less groundwater recharge and greatly increased surface runoff. In addition the waters available for recharge carry increased quantities of pollutants. With urbanization, waters having elevated contaminant concentrations also recharge groundwater including effluent from domestic septic tanks, wastewater from percolation basins and industrial waste injection wells, infiltrating stormwater, and infiltrating water from agricultural irrigation. The areas of main concern that are covered by this paper are: the source of the pollutants, stormwater constituents having a high potential to contaminate groundwater, and the treatment necessary for stormwater. METHODOLOGY An extensive literature review of stormwater pollutants that have the potential to contaminate groundwater was collected by searching prominent databases. This paper, a condensation of a larger, more detailed report (Pitt et a/. 1994), addresses the potential groundwater problems associated with stormwater toxicants and describes how conventional stormwater control practices can reduce these problems. Potential problem pollutants were identified, based on their mobility through the unsaturated soil zone above groundwater, their abundance in stormwater, and their treatability before discharge. This information was used with earlier EPA research results of toxicants in urban runoff sheet flows (Pitt and Field 1990) to identify the possible sources of these potential problem pollutants. Re mendations were also made for stormwater infiltration guidelines in different areas and monitoring that should be conducted to evaluate a specific stormwater for its potential to contaminate groundwater. RESULTS Sources of Pollutants. Tables 1 and 2 summarize toxicant concentrations and likely sources or locations having some of the highest concentrations found during an earlier phase of this EPA-funded research (Pitt and Field 1990). The detection frequencies for the heavy metals are close to 100% for all source areas, and the detection frequencies for the organics ranged from about 10% to 25%. Vehicle service areas had the greatest frequencies and/or quantities of observed organics. 222 TABLE 1. CONCENTRATIONS OF HEAW METALS IN OBSERVED AREAS Toxicant Highest Median (pg/l) Highest Observed (Pg/l) Cadmium Vehicle service area runoff 8 Streetrunoff 220 Chromium Landscaped area runoff 100 Roofrunoff 510 Copper Urban receiving water 160 Streetrunoff 1250 Lead CSO 75 Storage area runoff 330 NIckel Parking area runoff 40 Landscaped area runoff 130 Zinc Roof runoff 100 Roofrunoff 1580 TABLE 2 MAXIMUM CONCENTRATIONS OF TOXIC ORGANICS FROM OBSERVED SOURCES Toxicant Concentration Detection (PQ/L) Frequency(%) Significant Sources Benzo(a)anthracene Benzo(b)fluoranthene Benzo(k)fluoranthene Benzo( a) p yrene Fluoranthene Naphthalene Phenanthrene Pyrene Chlordane Butyl benzyl phthalate Bls(2chloroethyl)ether Bis(2chloroisopropyl)ether 1,3-0ichkmbenzene 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 preservatives Insecticide Plasticizer Fumigant, solvents, insecticides, paints, lacquers, varnishes Pesticide manufacturing Pesticide manufacturing Potential Contaminates to Groundwater. NUTRIENTS. Nitrates are one of the most frequently encountered contaminants in groundwater (AWWA 1990). Phosphorus contamination has not been as widespread or as severe as that of nitrogen compounds. Nitrate is highly soluble ( 1 kg/l) and will stay in solution in the percolation water. 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. The greatest pesticide mobility occurs in areas with coarsegrained or sandy soils without a hardpan layer, and with soils that have low clay and organic matter content and high permeability (Domagalski and Dubrovsky 1992). Pesticides decompose in soil and water, but the total decomposition time can range from days to years. In general, pesticides with low water solubilities, high octanol-water partitioning coefficients, 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 concem. OTHER ORGANICS. The most commonly occurring organic compounds found in urban groundwaters include phthalate esters and phenolic compounds. Polycyclic aromatic hydrocarbons (PAHs) have also been found in groundwaters near industrial sites. Groundwater contamination from organics occurs more readily in areas with sandy soils and where the water table is near the land surface (Troutman et al. 1984). 223 METALS. Studies of recharge basins receiving large metal loads found that most of the heavy metals are removed either in the basin by sedimentation or in the vadose zone. The order of attenuation in the vadose zone from infiltrating stormwater is: zinc (most mobile) lead cadmium manganese copper iron chromium nickel aluminum (least mobile) (Harper 1988). SALTS. Sodium and chloride used for deicing collects in the snowmelt and travels down through the vadose zone to the groundwater with little attenuation. Salts that are still in the percolation water after it travels through the vadose zone will contaminate the groundwater (Sabol et a/. 1987; and Bouwer 1987'). Studies of depth of pollutant penetration in soil have shown that sulfate and potassium concentrations decrease with depth, whereas sodium, calcium, bicarbonate, and chloride concentrations increase with depth (Close 1987; Ku and Simmons 1986). MICROORGANISMS. Viruses have been detected in groundwater where stormwater recharge basins were located short distances above the aquifer (Vaughn et a/. 1978). The factors that affect the survival of enteric bacteria and viruses in the soil include ph, antagonism from soil microflora, moisture content, temperature, sunlight, and organic matter (Jansons et al. 1989; and Tim and Mostaghim 1991). The major bacterial removal mechanisms in soil are straining at the soil surface and at intergrain contacts, sedimentation, sorption by soil particles, and inactivation. Treatment of Stormwater. Table 3 summarizes the filterable (dissolved solids) fraction of toxicants found in storm runoff sheetflows from many urban areas found during an earlier phase of this EPAfunded research (Pitt and Field 1990). Pollutants that are mostly in filterable forms have a greater potential of affecting groundwater and are more difficult to control with the use of conventional stormwater control practices which mostly rely on sedimentation and filtration principles. Fortunately, most of the storm-flow toxic organics and metals are associated with the nonfilterable (suspended solids) fraction. Possible exceptions include zinc, fluoranthene, pyrene, and 1,3-dichIorobenzene. Pollutants in dry-weather storm drainage flows, however, tend to be much more associated with filtered sample fractions and would not be as readily controlled with the use of sedimentation (Pitt et a/. 1994). TABLE 3. FILTERABLE FRACTIONS OF STORMWAER TOXICANTS FROM SOURCE AREAS Metals Filterable (%) Organics Filterable (%) Fraction Fraction Cadmium Chromium Copper Iron Lead Nickel Zinc 20 to 50 Benzo(a)anthracene 10 Fluoranthene 20 Naphthalene Small amount Phenanthrene c20 Pyrene Small amount Chlordane a Butyl benzyl phthalate Bis(2-chloroethy1)ethet Bis(2chloroisopropyl)ether 1,3-DichIorobenzene Irregular Irregular 75 Sedimentation is the most significant removal mechanism for particulate-related (nonfilterable) pollutants. Volatilization and photolysis are other important pollutant removal mechanisms in wetdetention ponds. Biodegradation, biotransformation, and bioaccumulation (into plants and animals) may also occur in larger and open ponds. Infiltration devices can safely deliver large fractions of the surface flows to groundwater, if carefully designed and located (EPA 1983). Grass-filter strips may be quite effective in removing particulate pollutants from overland flows. The filtering effects of grasses, along 224 with increased infiltration/recharge, reduce the particulate sediment load from urban landscaped areas. Grass swales are another type of infiltration device. CONCLUSIONS AND RECOMMENDATIONS With a reasonable degree of site-specific design considerations to compensate for soil characteristics, infiltration may be very effective in controlling both urban runoff quality and quantity problems (PA 1983). This strategy encourages infiltration of urban runoff to replace the natural infiltration capacity lost through urbanization and to use the natural filtering and sorption capacity of soils to remove pollutants: however, the potential for some types of urban runoff to contaminate groundwater through infiltration requires some restrictions. infiltration of urban runoff having potentially high concentrations of pollutants that may pollute groundwater requires adequate pretreatment or the diversion of these waters away from infiltration devices. The following general guidelines for the infiltration of stormwater and other storm drainage effluent are recommended in the absence of comprehensive site-specific evaluations: 0 Divert away from infiltration devices - dry-weather storm drainage effluent (probable high concentrations of soluble heavy metals, pesticides, and pathogenic microorganisms); combined sewage overflows (poor water quality with high pathogenic microorganism concentrations and clogging potential); snowmelt runoff (potential for having high concentrations of soluble salts); runoff from manufacturing industrial areas (potential for having high concentrations of soluble toxicants); and construction site runoff (high suspended solids (sediment) concentrations, which would quickly clog infiltration devices). 0 1, Runoff from other critical source areas (e.g., vehicle service facilities and large parking areas) should receive adequate pretreatment to eliminate the groundwater contamination potential before infiltration. 0 Runoff from residential areas (the largest component of urban runoff in most cities) is generally the least polluted urban runoff flow and should be considered for infiltration. Most past stormwater quality monitoring efforts have not adequately evaluated stormwater's potential for contaminating groundwater. These are the urban runoff contaminates with the potential to adversely affect groundwater (with the most prominent and/or analyses recommendations in parentheses): nutrients (nitrates); salts (chloride); VOCs (if expected in the runoff [e.g., runoff from manufacturing industrial or vehicle senrice areas] could screen for VOCs with purgeable organic carbon analyses); pathogens (especially enteroviruses, if possible, along with other pathogens [e.g., Pseudomonas aenrginosa, 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 total sample components (lindane and chlordane); other organics, as filterable and total sample components (1,3 dichlorobenzene, pyrene, fluoranthene, benzo(a)anthracene, bis(2-ethylhexyl)phthalate, pentachlorophenol, and phenanthrene); and heavy metals, as filterable and total sample components (chromium, lead, nickel, and zinc). The following urban runoff components can adversely affect infiltration and injection operations: sodium, calcium, and magnesium (calculate sodium adsorption ratio to predict clogging of clay soils); and suspended solids (determine the need for sedimentation pretreatment to prevent clogging). REFERENCES AWWA (American Water Works Association). Fertilizer Contaminates Nebraska Groundwater. A WA Mainstream. 34 (4): 6, Bouwer, Herman. Effect of Irrigated Agricutture on Groundwater. Jour. of Irriuation and Drainaue Enq. ASCE. 113 (1): , Close, M.E. Effects of Irrigation on Water Quality of a Shallow Unconfined Aquifer. Water Resources Bulletin. 23 (5): , Domagalski, J. L. and Dubrovsky, N. M. Pesticide Residues in Groundwater of the San Joaquin Valley, California. Joumal of Hvdroloqy. 130 (1-4): , EPA. Results of the Nationwide Urban Runoff Program. NTIS No. PB , U.S. Environmental Protection Agency, Water Planning Division, Washington, D.C., December Harper, Harvey H. Effects of Stormwater Management Systems on Groundwater Quality. Final Report for DER Project W190. Florida Department of Environmental Regulation, Jansons, J., Edmonds, L. W., Speight, 6. and Bucens, M. R. Survival of Viruses in Groundwater. Water Research. 23 (3): , Ku, H. F. H. and Simmons, D. L. Effect of Urban Stormwater Runoff on Groundwater beneath Recharge Basins on Long Island, New York. U.S. Geological Survey (USGS) Water Resources Investigations Report USGS, Denver, Colorado, Pitt, R., and Field, R. Hazardous and Toxic Wastes Associated with Urban Stormwater Runoff. -In: Proceedings of the 16th annual RREL Hazardous Waste Research Symposium: Remedial Action, Treatment and Disposal of Hazardous Waste. U.S EPA, Cincinnati, OH, EPA/600/ , Pitt, R., Clark, S. and Parmer, K. Potential Groundwater Contamination From Intentional and Non- Intentional Stormwater Infiltration. EPA/600/SR-94/129. U.S. EPA, Cincinnati, Ohio, Sabol, G. V., Bouwer, H. and Wierenga, P. J. Irrigation Effects in Arizona and New Mexico. Joumal of Irrigation and Drainage Engineering, ASCE. 113 (1): 30-57, Tim, U. S. and Mostaghim, S. Model for Predicting Virus Movement through Soil. Groundwater. 29 (2): , Troutman, D.E., Godsy, E. M., Goerlitz, D. F. and Ehrlich, G. G. Phenolic Contamination in the Sand-and- Gravel Aquifer from a Surface Impoundment of Wood Treatment Wastewaters, Pensacola, Florida. USGS Water-Resources Investigations Report USGS, Denver, Colorado, Vaughn, J.M., Landry, E.F., Baranosky, L.J., Beckwith, C. A., Dahl, M. C. and Delihas, N.C. Survey of Human Virus Occurrence in Wastewater Recharged Groundwater on Long Island. Amlied and Environmental Microbioloay. 36 (1): 47-51, FOR MORE INFORMATION: Richard Field, EPA Project Officer Chief, Storm and Combined Sewer Pollution Controt Program U.S. Environmental Protection Agency (MS-106) Edison, NJ (908)
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