Acid Rock Drainage From Highway and Construction Activities in Virginia, USA

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 <10 Mg CaCO 3 equivalent per 1000 Mg of material have been documented in various geologic settings. The vast majority of these potentially acidic materials occur outside of the coalfield region where acid drainage related issues have historically been concentrated. We have worked cooperatively with the Virginia Department of Transportation to: 1. develop a statewide sulfidic materials risk map; 2. document ARD impacts to soil and water quality and engineered structures; and 3. develop methods to assess site-specific risk potentials within a given highway corridor. A statewide sulfidic materials GIS risk map was developed based upon the state digital geology map which assigned four levels of relative risk to all mapped strata based upon predicted lime requirements and probabilities of encountering highly reactive materials. Non-highway construction activities have also routinely disturbed sulfidic materials, and a recent airport project in northern Virginia resulted in over 150 ha of extremely acidic (pH <3.5) post-construction soil materials that remained barren for over two years before being recognised as sulfidic. Acidic (pH 3.0; Fe >45 mg/L) run-off from this site heavily damaged a receiving stream, partially due to the fact that it dissolved the galvanised steel water control structures in stormwater detention basins, leading to direct discharge of run-off and sulfidic sediments. The airport area was treated and revegetated in 2002 with a combination of lime-stabilised biosolids, straw mulch, and acid-tolerant grasses. Water quality in a receiving second-order stream quickly responded to the treatment, but some release of N was also noted as a secondary effect. Collectively, these results point out the importance of accurately assessing the potential for excavation of sulfidic materials in construction environments, and the necessity of developing toxic materials handling strategies similar to those employed in mining environments.

Full text

Acid Rock Drainage From Highway and Construction Activities
in Virginia, USA
W L Daniels1and Z W Orndorff2
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 <10 Mg CaCO3equivalent
per 1000 Mg of material have been documented in various geologic
settings. The vast majority of these potentially acidic materials occur
outside of the coalfield region where acid drainage related issues have
historically been concentrated. We have worked cooperatively with the
Virginia Department of Transportation to:
1. develop a statewide sulfidic materials risk map;
2. document ARD impacts to soil and water quality and engineered
structures; and
3. develop methods to assess site-specific risk potentials within a given
highway corridor.
A statewide sulfidic materials GIS risk map was developed based upon
the state digital geology map which assigned four levels of relative risk to
all mapped strata based upon predicted lime requirements and
probabilities of encountering highly reactive materials. Non-highway
construction activities have also routinely disturbed sulfidic materials,
and a recent airport project in northern Virginia resulted in over 150 ha of
extremely acidic (pH <3.5) post-construction soil materials that remained
barren for over two years before being recognised as sulfidic. Acidic (pH
3.0; Fe >45 mg/L) run-off from this site heavily damaged a receiving
stream, partially due to the fact that it dissolved the galvanised steel
water control structures in stormwater detention basins, leading to direct
discharge of run-off and sulfidic sediments. The airport area was treated
and revegetated in 2002 with a combination of lime-stabilised biosolids,
straw mulch, and acid-tolerant grasses. Water quality in a receiving
second-order stream quickly responded to the treatment, but some release
of N was also noted as a secondary effect. Collectively, these results
point out the importance of accurately assessing the potential for
excavation of sulfidic materials in construction environments, and the
necessity of developing toxic materials handling strategies similar to
those employed in mining environments.
INTRODUCTION
In the eastern USA, the primary focus of concern over acid rock
drainage has been upon the Appalachian coal basin and
associated pyritic overburden and coal waste materials (Sobek,
Skousen and Fisher, 2000; Daniels and Stewart, 2000). However,
sulfidic deposits are found in various geologic and geomorphic
settings across the state of Virginia. In many of these settings,
road construction and other large scale land-disturbance has
resulted in localised acid rock drainage (ARD) problems.
Increasing development over the past several years, along with
constructed wetland excavation and the ever-deepening nature of
road cuts, has resulted in numerous new problem exposures of
acid-forming materials. While such problems historically had
been considered isolated occurrences, over the past decade the
Virginia Department of Transportation (VDOT) began to
recognise these sites as manifestations of the same underlying
cause. While huge sums of monies have been spent on these
combined problems in worldwide mining environments over the
years, none of the acid materials evaluation and mitigation
criteria from mining environments have been applied to the
construction and road planning and design process in Virginia.
In this paper we summarise major results and finding from our
multi-year study of VDOT highway corridor impacts (Orndorff,
2001), and the statewide distribution and characteristics of
acid-forming materials. We also focus upon a detailed review of
the nature and extent of soil and water quality impacts and their
remediation, at our largest impact site, the Stafford regional
airport. In addition to the work reported in detail in this paper, we
also conducted rigorous studies on:
1. the depth of sulfide oxidation as related to landscape
position and soil type; and
2. the inherent relationships among S-forms and various
potential acidity tests, which are not presented here, but are
detailed by Orndorff and Daniels (2002) and Orndorff
(2001).
RELATED STUDIES
Studies on the impact of ARD from highway construction focus
mainly on the generation of acid drainage and its effect on local
surface waters (Adams, Klamke and Hollabaugh, 1999; Fox,
Robinson and Zentilli, 1997; Igarishi and Oyama, 1999;
Mathews and Morgan, 1982; Morgan, Porak and Arway, 1982).
Less work has been completed on the deterioration of road
materials and related structures upon exposure to acid sulfate
weathering (Sahat and Sum, 1990; Vear and Curtis, 1981).
Most studies of the impacts of road construction through
sulfidic materials in North America have focused on water
quality issues. In 1963, reconstruction of US Highway 441 near
Great Smoky Mountains National Park involved cut and fill
operations in the Anakeesta formation – a sulfidic shale. The
demise of local aquatic life, in some areas reaching up to 8 km
from the highway, was attributed to indiscriminate use of pyrite
bearing rock as rip rap along the stream embankment (Huckabee,
Goodyear and Jones, 1975; Mathews and Morgan, 1982).
Construction beginning in 1965 of the Tellico-Robbinsville
Highway between Tennessee and North Carolina, also through
the Anakeesta shale, caused a similar decline in water quality. A
variety of remediation techniques, including NaOH additions at
the headwaters of affected streams, lime additions over selected
road embankments, and installation of soil blankets were applied
in the Tellico Wildlife Management Area in 1978, but all proved
to be minimally effective (Morgan, Porak and Arway, 1982).
Again, in 1978, disturbance of sulfidic shales during highway
construction in southeast Tennessee caused deterioration of
culverts, guardrails, and aquatic life. Rehabilitation, which
included placement of a sealant barrier and topsoil, revegetation,
and addition of alkaline solutions to affected streams, exceeded
the original highway cost (Anderson, Bell and Reynolds, 1991).
Halifax international airport in Nova Scotia provides another
dramatic example of adverse ARD impacts. Construction of the
airport between 1955 and 1960 exposed large volumes of
sulfide-rich slate of the Halifax formation from the Meguma
Group. Since that time, acid drainage has severely impacted
surrounding watersheds. Remediation efforts beginning in the
6th ICARD Cairns, QLD, 12 - 18 July 2003 479
1. Professor, Department of Crop and Soil Environmental Sciences,
Virginia Tech, Blacksburg VA 24061-0404, USA.
2. Post-Doctoral Research Associate, Department of Crop and Soil
Environmental Sciences, Virginia Tech, Blacksburg VA 24061-0404,
USA.
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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 H2O2oxidation/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 (<2 mm in
diameter) also were tested for pH in H2O and KCl. Water
samples from selected drainage locations were tested for pH and
for electrical conductivity (EC) using a Cole-Parmer conductivity
meter. Water subsamples were filtered, preserved with HNO3,
and analysed for Fe, Al, Mn, Cu, Zn, and S concentrations by
Inductively Coupled Plasma Emission Spectroscopy (ICPES).
Based on laboratory results for the geologic formations
evaluated in this study, and in conjunction with field observations
of acid sulfate weathering damage at specific locations, and with
consideration of standard vegetation management practices, a
sulfide hazard rating scheme was developed with four levels of
severity. Ratings are based on the proportion of samples for a
given formation with PPA and S values within defined ranges. A
statewide hazard map was produced by:
1. assigning the appropriate rating to each studied formation;
2. identifying the respective map unit on the geologic map of
Virginia for each formation;
3. colour-coding the four ratings; and
4. applying the code for each formation to its respective map
unit on a digital version of the geologic map of Virginia
using ARCViewTM Geographic Information Systems (GIS)
software.
An unpublished version of the digital geologic map was
provided by the Virginia Division of Mineral Resources (VDMR,
2001). Literature documented sulfide-bearing formations, not
evaluated in this study, are identified on the hazard map with a
fifth colour code.
Geologic, soil, and water samples from the Stafford airport site
in Northern Virginia were analysed by the same methods
discussed above.
RESULTS AND DISCUSSION
Characterisation of statewide sulfide hazard risks
The state of Virginia contains five distinct geologic/physiographic
regions:
1. the Atlantic Coastal Plain sediments;
2. Piedmont igneous and metamorphic rocks;
3. the Blue Ridge metamorphic and igneous complex;
4. the folded Valley and Ridge sedimentary rocks; and
5. the coal bearing Appalachian Plateau undeformed
sedimentary rocks.
Strata associated with documented acid roadcuts, and the
major problematic geologic formations identified in these five
regions are described in Table 1 and Figure 1. All sites exhibited
lack of vegetation due to very low pH of surface materials, and
numerous sites exhibited iron staining on concrete, deterioration
of concrete and metal construction materials (drainage ditches,
culverts, and guardrails), iron and aluminum precipitation in
streambeds, and sulfate salt efflorescence on roadcut surfaces.
For the purpose of this paper, we will focus our discussion on the
properties and interpretations associated with acid-forming
materials in the Coastal Plain and Piedmont provinces as they
have had the greatest impact to date on soil and water quality.
Full detail on all five geologic regions is provided by Orndorff
and Daniels (2002) and Orndorff (2001).
Atlantic Coastal Plain
Acid sulfate weathering problems in the Coastal Plain primarily
result from exposure of unconsolidated Tertiary marine
sediments, particularly those mapped as the Chesapeake Group
and Lower Tertiary deposits. These sediments occur in drab
shades of green, blue and grey, and consist of fine- to
coarse-grained, quartzose sand, silt, and clay that is variably
shelly, diatomaceous, and glauconitic (Rader and Evans, 1993).
Reflected light microscopy of polished sections from numerous
samples of Tertiary marine sediments indicated that sulfides
occur as abundant dispersed framboids, clusters of microcrystals,
and small, weathered, subhedral grains of pyrite. All forms were
present in all samples, and no major differences in morphology
or grain size were noted among the samples.
Analysis of samples from 23 deep borings throughout an area
of approximately 350 km2northeast of Richmond indicated that
completely reduced sediments have pH values ranging from
approximately 5.5 - 8.0, PPA values ranging from approximately
30 - 50 Mg CaCO3/1000 Mg material, and total-S values ranging
from approximately 1.0 - 2.5 per cent. Elevated total-S values
(>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.
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6th ICARD Cairns, QLD, 12 - 18 July 2003 481
ACID ROCK DRAINAGE FROM HIGHWAY AND CONSTRUCTION ACTIVITIES IN VIRGINIA, USA
Geologic formation (Region) Sample size Geologic samples Representative surface water drainage samples
PPA†%S pH Fe Al Mn Zn S
Dissolved – mg/L
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 <0.025 298
Quantico Slate (Piedmont) n = 13 32.7 1.09 2.61 114.2 66.9 17.4 3.5 639
Ashe Formation (Blue Ridge) n = 21 4.8 0.3 3.22 39.7 20.1 1.4 0.6 182
Devonian Black Shales (Valley and Ridge) n = 49 12.1 0.75 2.67 59 162.5 38.5 8.3 1011
† Mg CaCO3/1000 Mg material.
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.
FIG 1 - Sample locations from statewide survey of documented acid-sulfate roadcuts in Virginia, USA.

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 CaCO3/1000 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 CaCO3/1000 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
CaCO3/1000 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 CaCO3/
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 CaCO3/1000 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 CaCO3/1000 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.
482 Cairns, QLD, 12 - 18 July 2003 6th ICARD
W L DANIELS and Z W ORNDORFF
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.
TABLE 2
Sulfide hazard rating for evaluated geologic materials.

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
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
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.

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
<3.5. Surface salt concentrations and acidic seeps were
commonly observed.
Revegetation procedures
Based upon these collective findings, we recommended that the
site be variably limed to each sampling cell’s requisite CCE
requirement, fertilised appropriately, treated with an organic soil
amendment, and seeded to acid- and salt-tolerant grasses and
legumes based upon our experience with sulfidic coal waste
revegetation (Daniels and Stewart, 2000). In April and May of
2002, lime-stabilised biosolids (municipal sewage sludge) were
applied and incorporated across the entire site at varying rates
based upon their CCE (in dry biosolids) of 20 to 50 per cent, and
the site was seeded to a mixed herbaceous cover. This treatment
was designed to supply the full amount of lime required for
complete neutralisation of the potential acidity present in the soil
surface along with substantial organic matter and nutrient
loadings. The incorporated soil surface was then straw mulched
and hydro-seeded to a mix of acid- and salt-tolerant legumes and
grasses. Unfortunately, the spring and summer of 2002 were the
driest and hottest on record in eastern Virginia, and the
revegetation efforts largely failed. The site was reseeded in
September of 2002, however, and was fully revegetated (≥90 per
cent living cover) by late October of 2002. The exception was
highly acidic outcrop and seep areas on steep cut and fill slopes
that constitute <10 per cent of the site, and which will demand
intensive spot-liming and mulch treatments over time. Surface
soil samples indicated that the average post-amendment pH
across the site was >6.0.
Water quality effects
Beginning in February 2002, we collected surface and ground
water grab samples from 16 locations in and around the Stafford
airport site. Table 3 presents results for a subset of those
locations (see Figure 3) which portray the overall effects of the
airport disturbance and subsequent reclamation efforts on water
quality over the 2002 sampling year. Specifically, data are
reported for a small first-order stream as it enters the disturbed
area (SW 4), the same first-order stream at a point of maximum
acid water input within the site (SW 1), and as it discharges from
the airport (SW 6). We also present water data for the major
second-order receiving stream (Potomac Creek) upstream (SW 7)
from all airport inputs, and the main-stem of Potomac Creek
downstream (NRCS Dam). The NRCS Dam collection point is
from the outfall of a regional flood control impoundment that
integrates drainage from the entire 700 ha watershed including
the 150 ha impacted by the airport.
484 Cairns, QLD, 12 - 18 July 2003 6th ICARD
W L DANIELS and Z W ORNDORFF
1km00.5
Stafford Regional Airport Water
Quality Sampling Locations
N
FIG 3 - Overview of Stafford regional airport and water quality monitoring points reported. Locations SW4, SW1 and SW6 sample the
same stream sequentially as it flows into and through the site. Locations SW 7 and NRCS Dam sample the regional stream receiving
acid drainage.

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 <0.1 to 0.9 mg/L,
well below the drinking water standard (10 mg/L). The higher
nitrate-N values are associated with sampling points which are
also higher in ammonium-N as discussed below. Similarly,
ortho-P levels in discharge were quite low, generally less than
0.01 mg/L, which is notable since the biosolids that were
land-applied are relatively high in total and extractable P.
The only post-biosolids treatment water quality data of general
concern to date is the fact that the May through October 2002
samplings revealed significant levels of ammonia-N at the
discharge points from the two sediment control structures (3 to
18 mg/L) and at the discharge point from the NRCS Dam (16 to
18 mg/L). Pre-biosolids application values were always ≤1.0
mg/L at all locations, so we are certain that this is due to the
biosolids application on-site. Current USEPA (1999) water
quality criteria for ammonia-N indicate that all of our
observations at the downstream location (NRCS Dam) were
significantly less than acute toxicity criteria (eg 36 mg/L @ pH
7.0) but were approaching or significantly above the chronic
effects level of approximately 4.0 mg/L.
We assume that the ammonia-N levels in these waters were
high due to a combination of unique factors at this site. First, and
perhaps most importantly, is the very acidic initial nature of the
soils and waters involved, which can lead to a net positive charge
on the soil exchange complex which would repel the ammonium
ion (NH4+), leading to enhanced mobility in run-off. Microbial
soil and water nitrifier populations were also apparently inhibited
by the very low pH values and dry/hot environmental conditions
through the June 2002 sampling period. However, the drastic
drop in ammonia values in the October 2002 samples coupled
with the increase in NO3-N in run-off water confirms that active
nitrification was occurring on-site by September 2002. Further
sampling over the winter/spring of 2002/2003 (data not shown)
confirmed that that the ammonia-N levels in discharge waters
continued to drop to <1.0 mg/L.
Summary of airport impacts and remediation
treatment effects
Disturbance of approximately 150 ha of lower Tertiary sulfidic
Coastal Plain sediments produced an area of highly acidic soils
and run-off waters of historical significance in eastern Virginia.
Three years of untreated acid drainage from this site had
completely degraded various engineered water control structures
and lowered the pH of the main stem of the second-order stream
6th ICARD Cairns, QLD, 12 - 18 July 2003 485
ACID ROCK DRAINAGE FROM HIGHWAY AND CONSTRUCTION ACTIVITIES IN VIRGINIA, USA
Location Date pH EC
(uS/cm)
Fe Al S NH3-N NO3-N
(mg/L)
SW 4
(Above site)
5 Apr 5.12 121 6.1 0.5 2.3 ND 0.09
2 Jun 5.75 93 6.8 0.1 1.1 0.52 0.29
5 Nov 4.69 636 0.6 0.3 6.1 0.32 0.41
SW 1
(In site)
6 Feb 3.18 816 42 12 107 ND ND
5 Apr 2.93 1489 62 25 195 0.74 0.02
2 Jun 2.92 2080 67 7 294 46.5 ND
5 Nov 3.49 1496 34 17 252 3.95 8.69
SW 6
(Below site)
5 Apr 3.30 1267 42 18 147 0.88 ND
2 Jun 6.32 728 44 0.7 66 16.1 0.12
5 Nov 4.20 143 19 10 136 2.36 4.79
SW 7
(Above site)
7 May 5.48 58 2.9 0.2 4.8 0.13 0.05
2 Jun 6.60 56 2.4 ND 3.2 0.43 0.04
5 Nov 5.01 96 1.7 0.1 8.1 0.84 0.89
NRCS Dam
(Below site)
4 Mar 3.30 590 8.7 7.7 61 0.14 0.36
7 May 5.97 535 7.4 0.2 66 17.32 0.90
2 Jun 7.37 531 0.8 ND 57 18.34 0.08
5 Nov 5.23 962 0.3 1.0 138 1.86 12.8
TABLE 3
Surface water quality at five Stafford airport sampling locations at various dates in 2002. Lime-stabilised biosolids were applied to
reclaim the area in April and May 2002.

draining a much larger watershed to pH <3.5. The application of
relatively high rates of lime-stabilised biosolids to the acidified
soils on-site successfully buffered run-off waters into an
acceptable pH range and drastically reduced dissolved metal
loadings, but the multi-year efficacy of this treatment must be
confirmed.
Based upon other studies (Daniels et al, 2002), we expect
total-N losses from this site to decline drastically within one year
following application of the biosolids, but these data do point out
that N losses to surface- and possibly ground water are a likely
secondary effect of the use of heavy loading rates of
lime-stabilised biosolids on sites such this one. Earlier studies
(Daniels et al, 2001) indicated that N losses could be controlled
to a large extent through manipulation of the applied biosolids
C:N ratio through sawdust additions, albeit at considerable added
expense. Regardless, the net long-term water quality effects of N
losses must be weighed against both the environmental cost of
taking no action and the economic cost of purchasing and
applying agricultural lime, fertiliser and compost at
approximately $US 3000 per ha.
SUMMARY AND CONCLUSIONS
Excavation through sulfidic geologic materials during road
construction activities has resulted in ARD-related problems at
numerous discrete locations across Virginia. These problems can
be minimised, and even prevented, by incorporating sulfide
hazard analysis into the pre-design stage of highway
construction. Evaluating the likelihood of encountering sulfidic
materials can decrease exposure of problematic materials. When
exposure cannot be avoided, proper characterisation of the
material allows for immediate application of appropriate
remedial procedures.
Sulfide occurrence is a function of geologic setting. If sulfides
are identified in numerous rock samples from a specific geologic
formation, then the entire formation may be considered as ‘at
risk’ for containing sulfides. On a statewide scale, delineation of
potentially acid forming materials is best accomplished by
identifying the boundaries of sulfide-bearing formations using
the geologic map of Virginia. The specific geologic formations
associated with acid roadcuts were characterised by PPA and
total-S, and grouped into four final risk categories based on their
actual measured/documented potential acid-producing severity:
1. the Tabb Formation in the Coastal Plain (PPA ≤6 Mg
CaCO3/1000 Mg; S ≤0.2 per cent);
2. the Lynchburg Group of the Ashe Formation in the Blue
Ridge (PPA ≤18; S ≤2.0 per cent);
3. Chesapeake Group and Lower Tertiary deposits in the
Coastal Plain, and Millboro, Marcellus, and Chattanooga
shales, and the Needmore Formation in the Valley and
Ridge (PPA ≤60; S ≤2.6 per cent); and
4. Quantico slate in the Piedmont (PPA ≤99; S ≤3.9 per cent).
Additional sulfide-bearing formations were identified through
a geologic literature review, and were indicated on the map,
although the acid-producing severity of these materials has not
been evaluated. Where planned highway corridors intersect the
specified formations, detailed geologic sampling is essential to
identify the presence, extent, and nature of sulfidic materials.
Unfortunately, the most troublesome sulfide forms are
fine-grained, and as such, they are not readily apparent in hand
specimens and they often remain undocumented. Therefore, the
statewide sulfide hazard rating map reported here may be
considered to be the first approximation of a dynamic database
that can be amended by future studies. VDOT would benefit
tremendously from testing for total-S with depth and for PPA on
elevated S samples (>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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