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.

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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

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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

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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

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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

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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-

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    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)

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 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

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