Daniels and Orndorff, 2003 ICARD Acid Rock Drainage

Acid Rock Drainage From Highway and Construction Activities
in Virginia, USA
W L Daniels 1 and Z W Orndorff 2
ABSTRACT
Excavation through sulfidic geologic materials during construction
activities has resulted in acid rock drainage (ARD) related problems at
numerous (>40) locations across all five geologic regions of Virginia,
USA. Potential acidities ranging from >100 to

W L DANIELS and Z W ORNDORFF
early-1980s included capping of the waste rock pile with clay
and topsoil, a water treatment facility, wetlands, and other
experimental techniques. Initial remediation costs exceeded over
two million dollars, with operation and maintenance costing
about $US 240 000 annually since 1982. Nonetheless, acid
drainage from the airport and associated sites continues to be a
problem (Zentilli and Fox, 1997; Fox, Robinson and Zentilli,
1997; Hicks, 2003).
Perhaps the most critical step in characterising and managing
sulfidic materials is the development and testing of accurate
techniques for screening the acid-forming potential of geologic
materials. Extensive research has been conducted on this topic
over the past 30 years in various mining environments (Sobek,
Skousen and Fisher, 2000; Geidel and Caruccio, 2000), however,
the application of these same procedures to the diverse range of
sulfidic materials likely encountered in statewide road building
programs has not been documented.
METHODS AND MATERIALS
In the fall of 1997, a questionnaire regarding occurrence and
locations of acid roadcuts was distributed to all of the Virginia
Department of Transportation (VDOT) districts. All sites
reported (n = 27) as a result of this questionnaire were visited
over the following year. Over 20 additional sites were reported
later or discovered independently. Geologic materials and road
drainage grab samples, where available, were collected from all
sites. Both fresh and weathered representative samples of
lithologies at each site were obtained. The geologic formations
and specific rock types at all sites were determined through field
observations, personal communications with state geologists, and
geologic maps. All geologic samples were tested for potential
peroxide acidity (PPA) using the H2O2 oxidation/titration method
of Barnhisel and Harrison (1976) which is a variation of the
method described by O’Shay, Hossner and Dixon, (1990).
Total-S was determined with an Elementar Vario Max CNS
analyser, and rated for presence of carbonates by the HCl ‘fizz
test’ (Sobek et al, 1978), and pH in H2O and KCl using a
combination electrode. Surface samples from rock exposures that
contained a sufficient amount of soil-sized particles (0.2 per cent) were found at all locations indicating that S
occurrence may be ubiquitous in the Chesapeake Group.
Sediments containing carbonates have lower PPA values,
generally ranging from 0 - 20 Mg CaCO3/1000 Mg material, and
were found in only few samples from deep borings and not in
acid road banks. This suggests one of the following:
1. carbonate-bearing layers in the Tertiary marine sediments
tend to occur at greater depths;
2. excavation through carbonate-bearing sediments does not
result in severe ARD; or
3. carbonates have been leached out of existing roadcuts by
acid drainage.
480 Cairns, QLD, 12 - 18 July 2003 6th ICARD

ACID ROCK DRAINAGE FROM HIGHWAY AND CONSTRUCTION ACTIVITIES IN VIRGINIA, USA
TABLE 1
Summary of potential peroxide acidity (PPA) and per cent total-S levels for geologic samples, and pH and metal content of a road drainage
sample from representative sites. Note: The Appalachian Plateau Province was not specifically sampled by Orndorff (2001) and therefore
data are not presented here.
Geologic formation (Region) Sample size Geologic samples Representative surface water drainage samples
PPA † %S pH Fe Al Mn
Dissolved – mg/L
Zn S
Tabb Formation (Coastal Plain) n = 10 3.2 0.1 3.05 12.4 15.2 2.4 0.6 136
Tertiary Marine Sediments (Coastal Plain) n = 49 20.9 0.79 3.09 13.9 49.5 2.1

W L DANIELS and Z W ORNDORFF
Upon exposure, sulfide oxidation causes pH to decrease rapidly.
Weathered materials at the surface of roadcuts through the
Chesapeake Group and Lower Tertiary deposits typically appear
yellowish-brown, have pH values between 2.5 - 3.5, have PPA
values between 10 - 20 Mg CaCO 3/1000 Mg material, and retain
less than one per cent S. Less oxidised, underlying grey sediments
have slightly higher pH values and much higher PPA values,
ranging from about 30 - 50 Mg CaCO 3/1000 Mg material.
Acid sulfate weathering problems were less severe at a few
sites that are surficially mapped as the Sedgefield member of the
Pleistocene aged Tabb formation. The Sedgefield member
consists of fossiliferous brackish-bay sand, beach and near-shore
marine clayey sand, and lagoonal and marsh clay and clayey
sand. In our experience, materials with PPA values below 10 Mg
CaCO 3/1000 Mg are readily reclaimed with proper management,
while materials with PPA values between 10 - 60 require intense
reclamation management (Daniels, Li and Stewart, 2000).
Considering these guidelines, and the widespread occurrence of
S through the Chesapeake Group and Lower Tertiary deposits,
exposure of Tertiary marine sediments may be considered highly
likely to produce problematic roadside management conditions
which require intense reclamation efforts. Exposure of the
Sedgefield member of the Tabb formation may be considered
likely to produce moderately problematic roadside vegetation
management conditions, which could require special reclamation
efforts.
Piedmont Province
Acid roadcuts in Stafford County in Northern Virginia occur in
pyritic phyllite and slate of the Quantico Formation. Reflected
light microscopy of polished sections revealed the presence of
pyrite as corroded subhedral and euhedral grains, along with
chalcopyrite and covellite. Microcrystalline forms, such as those
described for Coastal Plain sediments, were not observed. The
PPA values for surface samples ranged from 6 - 22 Mg CaCO 3/
1000 Mg material, and S values ranged from 0.24 - 1.00 per cent.
One sample from relatively unweathered underlying material had
a significantly higher PPA value, 99 Mg CaCO 3/1000 Mg
material, and contained over 3.8 per cent S. Previous analysis of
six phyllite samples collected by VDOT in Stafford revealed PPA
values ranging from 1 - 85 Mg CaCO 3/1000 Mg material. These
values indicate sulfides are unevenly distributed throughout the
roadcut; however, more detailed sampling would be necessary to
characterise this spatial variability.
Compared to sulfidic sediments of the Coastal Plain, sulfide
levels in the Quantico Formation appear to be more variable and
occur over a much larger range of S values. With one exception,
drainage from this site had lower EC, and higher acidity and
metal concentrations, than any other evaluated roadcut. Exposure
of the Quantico Formation may be considered highly likely to
produce severely problematic roadside management conditions,
which require intense reclamation efforts. Roadcut surfaces of
the Quantico Formation may be quite steep and generally consist
of shallow, rocky, weathered material over bedrock, and rock
outcrops, which are less suited for standard soil remediation
methods than the unconsolidated sediments of the Coastal Plain.
Similar detailed information on acid-forming materials and
associated soil, water quality and engineered materials affects in
the other regions of Virginia can be found in Orndorff (2001) and
Orndorff and Daniels (2002). These reports also contain a full list
of all cited studies of sulfidic geologic and mine waste materials
in all five geologic provinces of Virginia.
Final compilation of a statewide sulfide hazard
rating map
The impact of acid drainage resulting from the exposure of
sulfidic materials during road construction depends on many
variables, including the relative volume of ARD moving to
surface stream flow, the flow rate of local surface waters, and the
neutralising capacity of surrounding geologic materials.
Although materials may be rated based on characteristics related
to S content, PPA, and rock drainage quality, the true risk of
environmental impact will depend on site-specific conditions.
With this in mind, the following scheme was developed to assess
geologic materials with general ratings in terms of sulfide
hazard. Materials were placed into four risk screening classes
based on PPA and total-S values:
1. materials for which 90 per cent of samples tested less than
10 Mg CaCO3/1000 Mg material and contained less than
0.5 per cent S;
2. materials for which 90 per cent of samples tested less than
10 Mg CaCO3/1000 Mg material and more than ten per
cent of the samples tested greater than 0.5 per cent S;
3. materials for which more than ten per cent of samples
tested greater than 10 Mg CaCO3/1000 Mg material and
less than ten per cent of samples tested greater than 60 Mg
CaCO3/1000 Mg material; and
4. materials for which more than ten per cent of the samples
tested greater than 60 Mg CaCO3/1000 Mg material.
These class boundaries were determined with consideration of
standard remediation methods and the observed properties of a
wide range of sulfidic materials. Application of these ratings to
the range of geologic materials evaluated in this study is shown
in Table 2. Again it should be emphasised that these ratings are
based strictly on the acid-producing potential of a particular
material, whereas actual acid production and severity of impact
will depend on site conditions. The overall distribution of all
scientifically documented acid-producing strata in the eastern
portion of Virginia is presented in Figure 2, which is a detailed
portion of the full statewide risk map produced by this study.
TABLE 2
Sulfide hazard rating for evaluated geologic materials.
Geologic map unit Sulfide hazard
rating †
Tabb formation – Sedgefield Member
(Coastal Plain)
1
Wise, Kanawha, Norton, New River, Lee and
Pocahontas Formations (Appalachian Plateau)
1
Ashe Formation of the Lynchburg Group
(Blue Ridge)
2
Chesapeake Group (Coastal Plain) 3
Lower Tertiary deposits (Coastal Plain) 3
Marcellus shale and Needmore Formation
(Ridge and Valley)
3
Millboro shale and Needmore Formation
(Ridge and Valley)
3
Quantico Formation (Piedmont) 4
Chattanooga Shale (Ridge and Valley) 4
† 1 = least severe, 4 = most severe.
482 Cairns, QLD, 12 - 18 July 2003 6th ICARD

Stafford airport case study
The Stafford regional airport site (see Figure 3) occurs directly
between two of the locations that were sampled and documented
in the VDOT corridor study described above. However, we were
unaware of its existence until 2001 due to a lack of direct VDOT
involvement in the construction and monitoring of the project.
This particular location was only reported to us after multiple
conventional revegetation efforts failed, and we were referred by
Virginia regulatory agency personnel. To our knowledge, this is
the largest single exposure of acid forming materials in the
eastern USA to date, other than that which occurred in the
unregulated era of Appalachian coal mining (pre-1977).
Construction activities at the site between 1998 and 2001
disturbed over 150 ha of lower Tertiary Coastal Plain materials as
the airport runway was constructed through a deeply dissected
landscape. As construction proceeded, long spur ridges were
excavated to depths ≥25 m, exposing significant volumes of grey,
reduced, sulfidic (0.6 to 1.2 per cent pyritic-S) silty sediments
which were subsequently filled into intervening valley fills to
ACID ROCK DRAINAGE FROM HIGHWAY AND CONSTRUCTION ACTIVITIES IN VIRGINIA, USA
FIG 2 - Geographic extent of sulfide-bearing geologic materials in the Coastal Plain of Virginia, USA.
support the >1500 m runway. Excavated sulfidic materials
exceeded the capacity of the valley fills and were also placed
into several large, steeply sloping excess spoil fills along a
first-order stream draining the eastern section of the site (see
Figure 3). Due to the fact that the sulfidic nature of these
materials was not recognised until well after all final grading was
completed, the acid-forming materials were not isolated away
from drainage, and in fact were essentially scattered randomly,
and thoroughly, throughout the site.
Soil acidity and associated site conditions
Inspection of the 10 to 15 m deep cut faces left uncovered along
the northern margin of the site in November 2001 revealed that
the upper 5 to 8 m of the soil-geologic column was pre-oxidised
by long term natural weathering processes, supported a soil pH
of 4.1 to 4.5, and was well-vegetated. However, below this
pre-oxidised depth, the soil pH in the weathered cut faces ranged
from 3.5 to 1.8, with prominent white salt efflorescences.
Fanning, Coppock and Rabenhorst (2002) also confirmed
6th ICARD Cairns, QLD, 12 - 18 July 2003 483

W L DANIELS and Z W ORNDORFF
occurrence of active acid-sulfate soil conditions on site. The
slopes were barren of vegetation and prominent acid rock
drainage was present. Concrete lined drainage ditches and
culverts were coated in iron and significant etching and
degradation of the cement components were noted. Galvanised
steel standpipes in water control structures in stormwater basins
below the site had also been completely degraded by the
drainage over time, releasing large volumes of sulfidic sediments
into the receiving floodplain. As discussed below, the acid
drainage from this site had seriously degraded surface water both
on- and off-site.
In December 2001, the existing surface soils were composite
sampled from 42 different locations across the site in association
with soil mapping requirements for remedial treatment. These
samples were analysed for soil:water pH and PPA as described
earlier. Soil pH ranged from a low of 1.80 to high of 5.28 with an
average of pH 3.05. Potential acidities ranged from -0.6 to -41.8
Mg calcium carbonate equivalence (CCE) per thousand Mg
material, with an average presumed lime requirement of 9.6 parts
per thousand or 21.5 Mg CCE per ha to an incorporation depth of
15 cm. It was clear from site mapping and detailed field
inspection that a few fill cells and surfaces at the airport site
received only minimal inputs of sulfidic materials. These areas
generally supported vegetation, were reddish to yellowish brown
in soil colour, and had soil pH values >3.8. However, the vast
majority of the site was completely barren of vegetation, was
characterised by grey (low chroma) soil colours, and soil pH

Location Date pH EC
(uS/cm)
SW 4
(Above site)
SW 1
(In site)
SW 6
(Below site)
Due to the naturally acidic nature of the soils within this
watershed, background surface water pH was typically less than
5.5, with moderate levels of dissolved Fe (Table 3). In general,
water quality discharging from the airport and from the NRCS
impoundment in early-2002 was highly acidified (pH 3.3 to 3.5)
and high in dissolved Fe, Mn, Al and S. Based upon comparison
with data from SW 7 and other control locations (data not
shown), there is no doubt that the airport construction had
significant negative water quality effects on Potomac Creek, and
upon an undetermined reach of the stream below the dam
discharge point due to the acidity and metals released over time.
Water samples taken subsequent to application of lime-stabilised
biosolids indicated that the pH of water discharging from the
on-site stormwater detention basins (eg SW 6) and the NRCS
floodwater structure sequentially increased into the 6’s and low
7’s, but then declined again somewhat by November, 2002.
Dissolved Fe in discharge waters ranged from 10 to 40 mg/L, and
ranged from 4 to 9 mg/L in early-2002 samples from the NRCS
Dam. By early June, however, the pH at the NRCS Dam was 7.3
with much lowered levels of metals. Sulfur levels remained
elevated, however, presumably due to the long-term release of
sulfate accumulated from the pyrite weathering reactions
associated with the site. However, our past experience in
coalfield acid mine drainage dynamics (Daniels, Li and Stewart,
2000) has indicated that seasonal (fall/winter) flushes of acid
reaction products from acid forming materials are possible.
Therefore, we cannot reach any firm conclusions regarding the
long-term effects of the lime-stabilised biosolids on site run-off
acidity and metal levels at this time.
Nitrate-N in all internal and discharge surface water samples
was low through August of 2002, ranging from

W L DANIELS and Z W ORNDORFF
draining a much larger watershed to pH 0.2 per cent) in all future road corridors
passing through known risk zones.
Once potentially acidic materials are exposed in cuts and
disposed of in oxidised fill environments (unsaturated), the
thermodynamics of pyrite oxidation will inevitably lead to acid
generation. In extreme examples, such as those found at the
Stafford airport, widespread soil and surface water acidification
and associated environmental damage will ensue. Currently, the
only known proven technique for permanently remediating these
situations is to bulk-blend lime or other alkaline materials with
the cut surface, or with the bulk of the disposal fill based upon
appropriate acid-base accounting procedures. Where feasible,
placement of the sulfidic materials below the:
1. water table; or
2 beneath an impermeable engineered cap will also
drastically limit or prevent acid generation.
Obviously, avoidance of sulfidic materials in the road planning
process is clearly the preferred mitigation alternative. However, it
is obvious that in many instances:
1. road corridors or construction projects cannot be
economically relocated sufficiently to miss sulfide-bearing
strata; and
2. the increasing depth of cut in modern road designs in
rolling topography will lead to increased probability of
intercepting sulfidic materials.
While the barren and erosive slopes resulting from
acidification of cut roadbanks are the most obvious indicator of
this problem, the long term emission of acidic drainage from fills
is clearly the most serious environmental compliance problem
that VDOT and other land developers will face with sulfidic
materials over time. It is clear that acid seepage from fills is
causing local damage to Virginia’s streams at various locations.
While the extent of this damage is very localised and not
extensive to date, the costs of capturing and treating these
discharges could represent significant long-term costs if and
when they are identified as point source discharges. Therefore,
the true cost of identifying, handling and disposing of potentially
acid-forming materials must be rigorously assessed and designed
for in the overall construction process.
ACKNOWLEDGEMENTS
We are indebted to the Virginia Transportation Research Council
(Mike Fitch and Mike Perfater) and to the District of Columbia
Water and Sewer Authority (Chris Peot) for their support of
various components of the work reported here. We also
appreciate the field support of Wright Trucking Inc. (Lloyd and
Milton Wright), Synagro (Steve McMahon), Adam Crist with
Stafford County, and the collective efforts of Campbell and Paris
(Tim Harms, Tony DiLuca, Cindi Martin and Ed Wallis) at
Stafford airport. Thanks also to Pat Donovan and Katie Haering
of Virginia Tech for assistance on the Stafford airport project.
Finally, we greatly appreciate the long-term persistence of Dr
Delvin Fanning of the University of Maryland in pointing out the
nature of acid-sulfate soils to our colleagues around the world.
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