Corrective Action Variance Application City of Raleigh Neuse River Wastewater treatment Plan Raleigh NC 12-01-2005 revised 03-31-2006

C orrective Action Variance Application
City of Raleigh
Neuse River Wastewater Treatment Plan
Raleigh, North Carolina
December 1, 2005
Revised March 31, 2006
MAR 3 1 2006
TABLE OF CONTENTS
Page
1.0 Introduction ........................................................................................................................ 1
2.0 Site Background and History ............................................................................................ 2
2.1 Site Description ...................................................................................................... 2
2.2 Site Physiography, Geology and Hydrogeology .................................................. 3
2.2.1. Regional Physiography .............................................................................. 3
2.2.2. Site Geology ................................................................................................ 3
2.2.3. Hydrogeology .............................................................................................. 4
3.0 Information Supporting Variance Request.. .................................................................. .4
3.1 Resolution ............................................................................................................... 4
3.2 Description of Past/Existing/Proposed Sources of Groundwater
Contamination ........................................................................................................ 4
3.2.1. Water Supply Wells ................................................................................... 5
3.2.2. Soil Sampling Results ................................................................................ 6
3.2.3. Groundwater Analytical Results .............................................................. 6
3.2.4. Surface Water Results ............................................................................... 6
3.2.5. Soil PAN Evaluation .................................................................................. 7
3.3. Description of the Proposed Variance Area ........................................................ 7
3.4. Public Health and Environmental Exposure ....................................................... 7
3.4.1. Groundwater .............................................................................................. 7
3.4.2. Surface Water ............................................................................................. 8
3.5. Economics of Available Technology ..................................................................... 9
3.5.1. Alternative 1: Groundwater Extraction and Enhanced
Denitrification along the Compliance Boundary and Discharge
to NRWWTP .............................................................................................. 9
3.5.2. Alternative 2: Groundwater Containment in Fields 50 and
500, Discharge to NRWWTP or Land Application, and Long-
Term Monitoring in Other Areas ........................................................... 11
3.6. Financial Hardship and Lack of Public Benefit.. .............................................. 12
3.7. Information Regarding Adjacent Property Owners ........................................ 13
4.0 Summary and Conclusions ............................................................................................. 13
5.0 References ......................................................................................................................... 14
LIST OF TABLES
Table 1: Private Well Nitrate Nitrogen Results and Water Supply/Service Status
Table 2: Soil Analytical Results
Table 3: Groundwater Analytical Results -City Test Wells
Table 4: Groundwater Analytical Results -CSA-SSA Monitoring Wells
Table 5: Surface Water Analytical Results
Table 6: Description of Proposed Variance Areas
Table 7: Projected Debited Total Nitrogen Allocation
Table 8: Neuse River Wastewater Treatment Plant Budget
LIST OF EXHIBITS
Exhibit 1: Nitrate Analytical Results
Exhibit 2: Human Health Risk Assessment -ENSR Consulting and Engineering (NC), Inc.
Exhibit 3: Ownership Information for Variance Parcels and Parcels Adjacent to Variance
Parcels
LIST OF FIGURES
Figure 1: Nitrate Analytical Results
Figure 2: Proposed Remediation Plan and Variance Areas
Figure 3: Private Wells within 0.5 miles of Neuse River Wastewater Treatment
Plant Spray Irrigation Areas
1.0 Introduction
This variance application has been prepared on behalf of the City of Raleigh Public Utilities
Department (CORPUD) to support CORPUD's request for approval of its Revised Corrective
Action Plan (CAP) to address nitrate contamination in groundwater at the biosolids application
fields serving the Neuse River Wastewater Treatment Plant (NRWWTP) in southeastern Wake
County.
In preparing the CAP, CORPUD evaluated various remedial alternatives to address nitrate
contamination at the site. CORPUD's evaluations focused on two alternatives. The first
alternative is one that fully complies with the Environmental Management Commission's (EMC)
rules and includes both hydraulically containing nitrate-impacted groundwater within the
compliance boundary and performing enhanced denitrification of groundwater beyond the
compliance boundary in areas where nitrate concentrations were predicted to exceed 10
milligrams per liter (mg/L). CORPUD determined that the capital and operation and
maintenance costs of this alternative over a thirty-year period would be nearly $80 million
dollars. Because of the economic infeasibility of the remedy, CORPUD explored alternative
remedies that would provide ample protection to human health and environment in an
economically reasonable manner.
As a result of this evaluation, CORPUD developed a second alternative remedy -its preferred
alternative -that provides for hydraulic containment of groundwater in the area with the highest
density of existing residences immediately downgradient of the land application fields together
with long-term groundwater monitoring and natural attenuation of nitrate levels for the
remainder of the site. This remedy would fully comply with the EMC's rules for corrective
action in 15A NCAC 02L .0106(k) ifCORPUD were a non-permitted facility. Since CORPUD
operates a permitted facility, this remedial alternative requires CORPUD to receive a variance
from the EMC's rules. Specifically, CORPUD requests a variance from 15A NCAC .0106(k)
that limits the applicability of that rule to non-permitted facilities. Additionally, CORPUD
requests a variance from the rule that requires permitted facilities to implement a clean-up,
recovery or containment plan to remedy violations of groundwater standards within the facility
when a violation of any standard in adjoining classified groundwaters occurs or can be
reasonably predicted to occur. See 15A NCAC 02L .0107(k)(3)(A).
CORPUD believes that its preferred alternative is fully protective of public health and the
environment, provided that nitrogen loading to the Neuse River via groundwater is addressed as
discussed in detail below. CORPUD does not believe the first alternative is economically
reasonable, particularly considering the minimal benefit gained from the substantial additional
expenditure. For these reasons, CORPUD believes that a variance from the rules of 15A NCAC
Subchapter 02L is appropriate and has prepared this document to support its request.
In addition to the information required by 15A NCAC 02L .0113(c), this document provides
background and historical information for the NRWWTP site in Section 2.0. Section 3.0
provides the following information that is required for the variance request:
(1) A resolution ofby the City of Raleigh requesting the variance.
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(2) A description of the past, existing or proposed activities or operations that have or
would result in a discharge of contaminants to groundwater.
(3) A description of the proposed area for which a variance is requested, including a
detailed location map, showing the orientation of the facility, potential for
groundwater contaminant migration, as well as the area covered by the variance
request, with reference to at least two geographic references.
(4) Supporting information to establish that the variance will not endanger the public
health and safety, including health and environmental effects from exposure to
groundwater contaminants.
(5) Supporting information to establish that requirements of Subchapter 02L cannot
be achieved by providing the best available technology economically reasonable,
including the specific technology considered, the costs of implementing the
technology, and the impact of the costs on the applicant.
( 6) Supporting information to establish that compliance would produce serious
financial hardship on the applicant.
(7) Supporting information that compliance would produce serious financial hardship
without equal or greater public benefit.
(8) A list of the names and addresses of any property owners within the proposed area
of the variance as well as any property owners adjacent to the site covered by the
vanance.
A summary of this variance application and conclusions is presented in Section 4.0, and
references are located in the final section.
2.0 Site Background and History
2.1. Site Description
The NRWWTP consists of approximately 1,466 acres of mostly contiguous farmland owned or
leased by CORPUD and divided into numbered fields. Properties surrounding the Site consist of
residential properties, farmland, and state-owned forestland. The northern and eastern Site
boundaries border a 3.6-mile section of the Neuse River. Beddingfield Creek bounds the Site to
the south. Topographically, the Site ranges in elevation from an approximate high of 270 feet
above mean sea level (ft msl) in upland areas to an approximate low of 140 ft msl at the Neuse
River (ENSR, 2002). A layout of the facility, associated biosolids application fields and the
current compliance boundary are depicted on Figure 1.
The Neuse River is classified as a Class C NSW (nutrient sensitive water) from the Falls Lake
Dam to the mouth of Beddingfield Creek. From the mouth of Beddingfield Creek to
approximately 0.2 miles downstream of Johnson County State Road 1700, the Neuse River is
classified as Water Supply V Nutrient Sensitive Water (NSW). Beddingfield Creek is classified
as C NSW from the source to the Neuse River. No nitrate water quality standard has been
established for class C NSW surface water. For surface waters classified as Water Supply V
NSW, nitrate water quality standard is 10 mg/L.
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2.2. Site Physiography, Geology and Hydrogeology
2.2.1. Regional Physiography
The Site is situated within the eastern Piedmont Physiographic Province of North Carolina. Area
topography consists of rolling hills dissected by narrow v-shaped drainage ways and perennial
streams that drain into Neuse River. Localized steep bluffs exist to the south along Beddingfield
Creek and along the Neuse River to the east and north of the Site (May and Thomas, 1965).
Localized bluffs in this area plateau to narrow bench cut alluvial floodplains that are nearly flat
with incised drainage ways to the Neuse River.
2.2.2. Site Geology
The Site is within the Raleigh Geologic Belt and the underlying bedrock consists of massive
granitic rock of the Rolesville series. The granitic bedrock is part of an intrusive series described
as megacrystic to equigranular and is dated between 270 and 320 million years old
(Pennsylvanian to Permian). Mafic dikes have been identified regionally and generally have a
northwest to southeast alignment. According to published literature, these dike features may be
up to 100 to 200 ft wide. Smaller dike splays may be 10 to 20 ft wide (Parker, 1979). Details of
the dikes and geologic maps can be found in the SSA (ENSR, 2003).
Lithologic units identified at the Site are typical oflocal piedmont geology and include the
following:
• Topsoil and weathered parent rock material, referred to as saprolite tends to be
moderately thick in locations without visible rock outcropping. Site saprolite consists of
yellow brown to orange sandy silts (ML) to silty sands (SM) with the coarser material at
depth. Regionally, saprolite can vary in thickness from a few feet to up to hundreds of
feet. Saprolite typically contains relict structures and fabric from the parent rock from
which it has weathered. Saprolite thickness at the Site commonly ranges between 30 and
60 feet below surface grade (bsg).
• Partially weathered rock (PWR), often referred to as the transition zone between saprolite
and the parent unweathered bedrock, often exhibits the same properties as deeper
saprolitic soils (SM) but with higher occurrence of rock and rock fragments. PWR
thickness often ranges from 0 to 10 ft thick on ridges and uplands to 10 to 20 ft thick
along slopes and low-lying areas (Wilson and Carpenter, 1981).
• Bedrock in this area typically consists of granitic rock with fractures near the interface of
PWR and bedrock. The number and size of the fractures generally dissipate with depth
while voids and vugs are common in shallow rock zones when weak exfoliation soil
zones are encountered near PWR.
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2.2.3. Hydrogeology
Hydrogeologically, the Site is situated in a meta-igneous hydrostratigraphic unit of the eastern
Piedmont of North Carolina (Daniel and Payne, 1990). Two general hydrostratigraphic units
(saprolite and PWR/upper bedrock) characterize the regional hydrogeology. The upper saprolite
unit.is an unconfined aquifer that transmits water downward to the lower semi-confined PWR
and fractured confined crystalline bedrock aquifer unit. Groundwater yields often range from 2 to
20 gallons per minute (gpm) within the unit (Daniel and Payne, 1990). Groundwater occurs
where saprolite and localized sedimentary/alluvial deposits along the Neuse River overlie
bedrock. Groundwater movement in the saprolite is typographically controlled by groundwater
divides associated with ridges and streams. Typically flow of groundwater occurs from upland
areas (ridgelines) to perennial streams. The underlying granitic rocks are known to have lower
hydraulic conductivities than either saprolite or PWR and controls deep groundwater or regional
groundwater flow conditions. The PWR lies between saprolite and bedrock units and
groundwater movement flows both within the material matrix and through fractures.
Groundwater movement in bedrock is restricted to intersecting sets of water-bearing fractures
and joints (Hamed and Daniel, 1989).
Hydraulic properties of the saprolite and PWR zones were evaluated using rising and falling
head slug test methods. Hydraulic conductivity (K) values for the shallow aquifer ranged from
1.3 x 10-6 to 6.4 x 10-3 centimeters per second (cm/sec). K values for PWR wells ranged from
4.4 x 10-5 to 1.1 x 10-3 cm/sec. A transmissivity of 4.6 x 10-5 square centimeters per day
(cm2/day) (1.3 square feet per day [ft2/day]) was obtained for well MW-126d (ENSR, 2003).
Quantification of groundwater flow directions and rates has been provided by a calibrated, three-
dimensional groundwater flow model. Quantification of the movement and discharge locations
of nitrogen originating from the biosolids fields has been provided by a three-dimensional
transport model that uses the flow model to compute groundwater velocities. Both of these
models are documented in the Comprehensive Site Assessment and Supplemental Site
Assessment, and have been reviewed and approved by the Aquifer Protection Section.
3.0 Information Supporting Variance Request
3.1. Resolution
In accordance with 15A NCAC 02L .0113(c)(a), the Raleigh City Council (Council) has made
this request for a variance to the EMC's rules. A copy of the Council's resolution to this effect is
attached as Exhibit 1.
3.2. Description of Past/Existing/Proposed Sources of Groundwater
Contamination
CORPUD has been operating the NRWWTP in southeastern Wake County since 1976. It began
land-applying biosolids in 1980 under a land application permit (Permit# WQ000l 730) issued
by the North Carolina Division of Water Quality (DWQ). The permit allows for the application
of 7,000 total dry tons of Class B Biosolids per year on fields listed in the permit. Figure 1
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depicts fields to which CORPUD has land-applied biosolids under its permit. Since 1980, fields
have been added and removed from the biosolids application program. For example, CORPUD
discontinued biosolids application on Fields 1, 2 and 3 in 1998 and the City converted them into
a police training facility. Several fields (Fields 100, 101,102,200,201,500, 512,513,522,523
and 524) were formerly leased for biosolids application but are no longer leased for this purpose.
The property containing former leased Fields 100, 101, 102, 522, 523, and 524 is currently
owned by Waste Corporation of America and is used as a construction and demolition landfill.
CORPUD currently leases fields 600,601,602 and 603. The remaining fields shown on Figure
1 are owned by CORPUD.
Groundwater quality monitoring required under the permit revealed exceedances of NCAC
Subchapter 02L nitrate groundwater standard in proximity to the compliance boundary of
CORPUD-owned biosolids application fields. The City suspended all land application of
biosolids in September 2002 (ENSR, 2003). The following sections discuss groundwater
contamination at the Site.
3.2.1. Water Supply Wells
In 2002, CORPUD sampled thirty-six private water supply wells located in the vicinity of the
Site. Analytical data indicated that seven wells had nitrate concentrations in excess of 10 mg/L
(see Table 1). The source of nitrates detected in these wells was likely a combination of septic
systems, non-CORPUD fertilization ofupgradient fields, and biosolids application to upgradient
fields. CORPUD subsequently initiated a quarterly sampling program of private water supply
wells located within a half of a mile of the biosolids application field boundaries. The City
identified forty-five private and/or community water supply wells and included them in the
sampling program. A summary of the wells identified within proximity of the Site and
associated analytical results (from CORPUD sampling program) are listed in Table 1. Thirty-
nine of the forty-five properties included in the sampling program were subsequently connected
to the public water supply system. These thirty-nine properties were served by thirty-eight water
supply wells, of which thirty-seven wells have been decommissioned consistent with the NCAC
Subchapter 02L requirements. Per the information provided by CORPUD, the residential
property with the remaining private water supply well has been connected to the public water
supply system; however, the well will not be abandoned as requested by the property owner.
Based on the information provided by CORPUD, there are three private water supply wells
(identified as PW-24, PW-42, and PW-43 in Table 1) that are still in use (active) and remain in
the CORPUD sampling program. Nitrate concentrations for these currently active water supply
wells were below 10 mg/L during the January 2005 sampling event (see Table 1). These wells
are not likely receptors for nitrate-impacted groundwater migrating from the biosolids
application fields. CORPUD will continue to monitor the three remaining wells as long as
required under its land application permit.
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3.2.2. Soil Sampling Results
Analytical results of the soil samples collected from Fields 3, 100, and 500 are summarized on
Table 2. The data indicate concentrations of nitrate generally peak in 4 to 8 ft depth interval
(ENSR, 2002). The soil profile nitrate concentrations are expected to change over time, but the
peak concentrations are likely to stay in approximately same depth interval. The implication of
this feature is that nitrates are accumulating at the 4 to 8 ft depth interval through mechanisms
such as infiltration redistribution (some water takes a rather slow pathway through the soil) and
anion exchange (nitrate is an anion).
3.2.3. Groundwater Analytical Results
Groundwater analytical data for the CORPUD test wells and the CSA-SSA wells are provided in
Tables 3 and 4, respectively. The groundwater analytical data is depicted in Figure 1. The data
indicated that nitrate exceeded its 02L groundwater standard at locations near the compliance
boundary in the areas of Fields 6, 12, 18, 19, 41, 47, 50, 60, 61, 62 63, 74, 100,201, 500, and
503. The deep saprolite well (MW-113d) and bedrock wells (MW-lOld, MW 105d and MW-
11 ld) also exceeded nitrate groundwater standard (ENSR, 2002).
Analytical results suggest a potential for nitrates from biosolids application in Field 50 to have
impacted groundwater on the residential property to the east and in the former private water
supply well (PW-22). Field 50 received biosolids routinely between 1982 and 2002 and has been
reported to have received excess PAN applications in 8 of those years (ENSR, 2002). Results
from assessment of Field 500 suggested a more limited potential for nitrate impacts from
biosolids application.
Off-site nitrate impacts to groundwater associated with biosolids application in the vicinity of the
intersection of Old Baucom Road and Mial Plantation Road does not appear to extend
significantly east of Shotwell Road or Mial Plantation Road. Nitrates in groundwater exceeded
the nitrate groundwater standard within Field 500 in the vicinity of former private water supply
wells PW-8, PW-12, PW-30, and PW-36. The application history for Field 500 indicates that
biosolids application to Field 500 ceased in 1994 and that biosolids application rates were
generally less than other application fields such as Field 50. Field 500 apparently has been
cropped several years before and after biosolids application. The SSA concluded that detected
nitrates in groundwater in Field 500 were not due to biosolids application alone (ENSR, 2003).
Analytical data from wells located across major streams such as Beddingfield Creek indicated
that migration of nitrate impacted groundwater under the stream is likely not occurring (ENSR,
2003).
3.2.4. Surface Water Results
Surface water analytical results are tabulated in Table 5 and depicted on Figure 1. The surface
water data from several samples collected in first order tributaries and seeps within the
application areas had nitrate concentrations above 10 mg/L. Nitrate in surface water suggests
6
groundwater discharges to the streams and tributaries (ENSR, 2002). Nitrate in samples
collected from Beddingfield Creek and the Neuse River were lower and did not exceed 10 mg/L.
3.2.5. Soil PAN Evaluation
An incubation study was conducted as part of the SSA to estimate the amount of PAN in soils
from fields at the NRWWTP and the residual PAN for the 2003-growing season. The 2003 soil
PAN evaluation indicated that many of the fields in the study area could supply adequate to
excessive amounts of PAN for crop production. The evaluation indicated that approximately 38
fields would supply PAN in excess of the amount required for anticipated crop production in
2003 (ENSR, 2003).
3.3. Description of the Proposed Variance Area
The location of the areas proposed for a variance from the standards of 15A NCAC 02L is
depicted on Figure 2 with hatching or cross hatching ( cross hatching denoting areas that will
receive active remediation). The parcels containing variance areas are colored green and labeled
as parcel numbers 119 through 155. Most of the variance area is not currently owned by
CORPUD. The actual land uses for each parcel are provided in Table 6. The parcels for which a
variance is requested are primarily rural, agricultural or forested lands. While some of the
parcels have private residences (i.e., Parcels 121, 122, 126, 129, 131, 134, 138, 141, 143, 146
through 148, 150 through 152, and 155), the majority of the land for which a variance is
requested is vacant. The land south of Beddingfield Creek at the southern portion of the site
(Parcels 119, 139 and 140) comprises a portion of Clemmons State Forest. The large parcel to
the west of site (Parcel 130) is owned by Waste Corporation of America (WCA) and is currently
used as a construction and demolition debris landfill. Parcel 137 to the east of the site is a
cemetery. All of the properties for which a variance is requested, except Parcels 119, 130, 139
and 140, have public water service or access to public water service should a residence or place
of business be constructed on the parcel. Only the WCA parcel and Parcel 134 (an individual
residence) use well water from the vicinity of the site, though for non-potable uses exclusively.
3.4. Public Health and Environmental Exposure
ENSR prepared a baseline human health risk assessment on behalf of CORPUD to evaluate the
potential risk to human health from nitrate-impacted groundwater at the site. A copy of this risk
assessment is attached as Exhibit 2. The following sections discuss the potential receptors and
exposure routes at the site and evaluate the potential risks to public health under several
conservative exposure scenarios. It also discusses the measures that CORPUD will take to
ensure protection of surface water in the vicinity of the site if its variance request is granted.
3.4.1. Groundwater
All wells within a half-mile radius of the site are shown on Figure 3. Well construction
information for these wells is not available. In 2002, CORPUD instituted a testing program for
nearby private water supply wells that were likely to impacted by nitrate-contaminated
groundwater from the site. Since that time, most water supply wells at nearby residences have
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been replaced with public water supply and the former water supply wells have been abandoned.
(ENSR, 2005; ENSR, 2003). CORPUD offered free connections and water service to all
properties within its testing program, regardless whether the well serving that property had
experienced an exceedance of the groundwater standard and regardless whether there was any
evidence of or potential for contamination of the well by nitrate-contaminated groundwater
emanating from the CORPUD biosolids application fields. There are three private water supply
wells originally in the testing program that are currently in use but nitrate concentrations in those
wells are below the nitrate groundwater standard. See Figure 3. The remaining wells shown on
Figure 3 that were not part of CORPUD's testing program are at no risk from nitrate-
contaminated groundwater as indicated by CORPUD's conservative groundwater models.
To provide a conservative estimate of potential risks, ENSR evaluated potential future use of site
groundwater or downgradient groundwater by considering a hypothetical future resident
potentially exposed to nitrate in groundwater used as drinking water. For non-potable uses,
ENSR considered a hypothetical future resident using groundwater for a swimming pool. The
receptor evaluated was a young child (aged 0-6 years) as a child is the most sensitive receptor for
noncarcinogenic effects. ENSR considered both ingestion and dermal routes of exposure.
Further details of the methods and data used and assumptions made are found in ENSR's report
in Exhibit 2. After calculating the noncarcinogenic hazard indices (HI) and comparing it to the
BP A index, ENSR found that there were no unacceptable risks for exposure to groundwater used
for a non-potable purpose (swimming pool). The His also indicated that there were no
unacceptable risks for using groundwater for irrigation purposes. The His for potable use of
groundwater indicated a potentially unacceptable risk for site groundwater if it were used as
drinking water. However, no property owners in the vicinity of the NRWWTP are using
groundwater for drinking water that exceeds the nitrate groundwater standard or is predicted to
exceed the standard. Moreover, the City will monitor nitrate levels in groundwater at the
compliance boundary for as long as nitrate concentrations in groundwater are above the 10 mg/L
standard to ensure the protection of human health and the environment.
3.4.2. Surface Water
Nitrate was detected in Beddingfield Creek and in other tributaries to the Neuse River. The
NRWWTP site is partially fenced, which may reduce unauthorized access and use of the site.
However, it is possible that a trespasser or nearby resident might wade in one of the tributaries to
the Neuse River, located within the site or in Beddingfield Creek. To ensure a conservative risk
assessment, the receptor was identified as a child or teenager (aged 7 to 16 years) wading in the
surface water. As with the non-potable use of groundwater, ENSR found that there were no
unacceptable risks for exposure to surface. See Exhibit 2.
Nor does the nitrate contamination in groundwater present a localized risk to surface water
quality or aquatic life. In order to protect the Neuse River estuary from any increased risk of
eutrophication, CORPUD has agreed that, as a condition of the variance, it will accept a
condition in its wastewater discharge permit to account for the amount of nitrogen estimated to
enter the Neuse River from groundwater in excess of the nitrate groundwater standard.
CORPUD is currently allowed to discharge 676,496 pounds of nitrogen per year to the Neuse
River, but its actual discharge is substantially below the permitted amount. Under the proposed
8
permit condition, CORPUD will be required to count toward its annually-reported amount of
discharged nitrogen not only the amount actually discharged by the NR WWTP, but also the
annual amount the model predicts will be discharged to the Neuse River via groundwater as a
result of the violations of the groundwater standard for nitrate. The model conservatively
indicates that the amount of this additional nitrogen discharge will be 123,000 pounds in 2006
and will decrease approximately 3,000 pounds per year. Table 7 illustrates the effect of this
nitrogen debit over time. The debit can be adjusted to reflect actual field conditions and would
be eliminated whenever all monitoring wells come into compliance with the standard. As a
result of this condition, CORPUD's wastewater treatment and disposal operations at the
NRWWTP will never contribute more nitrogen to the Neuse River than is currently allocated.
3.5. Economics of Available Technology
In determining an appropriate CAP for the nitrate contamination at the NRWWTP site, ENSR
identified potentially applicable technologies and evaluated alternatives for containing and
treating nitrate-impacted groundwater at the site (ENSR, 2005). ENSR completed a detailed
evaluation of a remedial alternative that uses best available technology and achieves full
compliance with the EMC's rules for groundwater corrective action (Alternative 1). This
remedy would include both hydraulically containing nitrate-impacted groundwater within the
compliance boundary and denitrification of groundwater beyond the compliance boundary in
areas where nitrate concentration were predicted to exceed 10 mg/L. Monitoring to evaluate the
effectiveness of the system would occur for at least 30 years, the expected life of the project.
The capital and operation and maintenance costs of this alternative over a thirty-year period
would exceed $68 million dollars.
Alternative 2, CORPUD's preferred alternative, provides for hydraulic containment of
groundwater in the area with the highest concentration of existing residences immediately
downgradient of the land application fields together with long-term groundwater monitoring and
natural reduction in nitrate levels for the remainder of the site.1 This remedial alternative
requires CORPUD to receive a variance from DWQ's rules. Alternative 2 would cost
approximately $9 million dollars to implement -$70 million dollars less than Alternative 1 -and
provide ample protection of human health and the environment. The following sections present
the details and these remedial alternatives and their associated costs.
3.5.1. Alternative 1: Groundwater Extraction and Enhanced Denitrification
along the Compliance Boundary and Discharge to NRWWTP
Extraction System Process. Based on hydro geologic data and results of groundwater flow
modeling, it is anticipated that approximately 426 extraction wells (100-ft spacing) would be
1 CORPUD believes that a variance could be justified that required no active remediation. However, DWQ
indicated early in this process that its support for a variance request would be conditioned upon the CAP including
active remediation in the area with the highest concentration of downgradient residences, and CORPUD has agreed
to that condition.
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installed along the portions of the compliance boundary where the nitrate groundwater standard
has been exceeded and/or is estimated to be exceeded based on groundwater modeling. The
depth of extraction wells would be expected to vary in different areas of the Site based on
elevation and water table. For purposes of developing probable costs, the average depth for the
wells is assumed to be 70 ft bsg. The average groundwater yield from these wells would be 2
gpm (1,226,880 gallons per day) which would be pumped through a network of extraction piping
to the NRWWTP for treatment. The piping required to convey water to the NRWWTP is
assumed to be installed underground, in trenches, along the roads and fields. The design,
construction, start-up, and decommissioning costs of this alternative are estimated to be
$19,220,060. Operation and maintenance costs, including treating the extracted water, would
cost approximately $29,868,120 over 30 years. The present worth of the costs associated with
the groundwater extraction system is approximately $30,727,827.
Enhanced Denitrification System Process. The enhanced denitrification process involves
injection (pressure or gravity feed) of biodegradable carbon electron donor (e.g., com syrup or
sodium lactate) via injection wells to create in situ anaerobic zones that would denitrify nitrate-
enriched groundwater in plumes situated beyond the compliance boundary across the Site. The
electron donor injection allows the populations of native microorganisms to multiply to the point
where microbial respiration consumes the available dissolved oxygen in groundwater. In the
absence of dissolved oxygen the microbes would use nitrate as an electron acceptor and produce
nitrogen gas, a process referred to as denitrification. Nitrate-impacted groundwater from the
application fields that migrates into the anoxic zone would be exposed to the denitrifying
bacteria and pass through the anoxic zone with little to no nitrate remaining in the water.
Prior to implementing a full-scale in-situ denitrification system, a pilot test would have to be
conducted to evaluate the effectiveness at the Site and to collect data for full-scale design.
Injection wells would be constructed within the compliance boundaries of the above-referenced
fields to reduce nitrate concentrations in the impacted groundwater. ENSR estimated that
approximately 195 injection wells would be required to achieve this control. Injection wells
would be properly spaced to allow establishment of anaerobic zones to support denitrification.
ENSR also anticipates that the injection wells would be installed to depths ranging from 65 to 85
ft bsg using conventional drilling techniques. This process would involve preparing the electron
donor solution by mixing the required amount of electron donor (e.g., com syrup or sodium
lactate) with appropriate amounts of potable water. The electron donor solution would then be
manually injected into injection wells by either gravity feeding or pumping.
This remedy would require a field-scale pilot study to estimate the quantities of electron donor
solution and to determine the design parameters ( e.g., area of influence, spacing and number of
injection wells/points, frequency of injection) prior to designing a full scale system. For the
purpose of costing, ENSR estimated that electron donor solution would be injected quarterly for
two years.
ENSR determined that the probable costs for the denitrification portion of Alternative 1,
including capital costs, operation and maintenance, and short-term monitoring, would be
$27,769,400, which has a present worth of $25,401,200.
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Monitoring. To monitor effectiveness of Alternative 1, approximately 20 monitoring wells,
20 injection wells, and 10 surface water locations would be sampled three times a year and
analyzed for nitrate for the life of the project. In addition, 20 samples would be analyzed
annually for biogeochemical parameters (i.e., ferrous iron, total organic carbon etc.) to evaluate
denitrification/anaerobic conditions. ENSR estimated that 88 recovery wells would be sampled
annually for nitrates. It should be noted that CORPUD currently samples the compliance wells
three times a year as part of the compliance monitoring. Test well data would be used in
evaluating the performance of this alternative. The actual cost of the long-term monitoring (30-
year) program would be approximately $3,024,000, with a present worth of$1,382,373.
3.5.2. Alternative 2: Groundwater Containment in Fields 50 and 500,
Discharge to NRWWTP or Land Application, and Long-Term
Monitoring in Other Areas
Based on the available information, and groundwater flow and transport modeling, nitrate
concentrations have exceeded the groundwater standard at or beyond the compliance boundary
for Fields 50 and 500. This alternative is intended to control further off-site migration of nitrate
impacted groundwater from these areas. Long-term monitoring only is proposed for the
remaining areas of the site where exceedances of nitrate groundwater standard have occurred at
or beyond the compliance boundary.
Groundwater Extraction Process. Alternative 2 involves the collection of nitrate-impacted
groundwater using appropriately-spaced extraction wells in Fields 50 and 500. The groundwater
extraction (recovery) wells would be installed within the compliance boundaries in these two
fields to allow containment of the dissolved nitrate plume exceeding nitrate groundwater
standard. These extraction wells are expected to be installed to depths ranging from 60 to 80 ft
bsg. Based on hydrogeologic data and results of the groundwater capture zone modeling, ENSR
determined that 7 extraction wells would be installed near the eastern compliance boundary of
Field 50 to a depth of approximately 80 ft bsg. In addition, 22 extraction wells would be
installed near the eastern compliance boundary of Field 500. The depth of extraction wells in
Fields 500 is approximately 60 ft bsg. Figure 2-2 presents a layout of the proposed extraction
wells. Based on the results from the aquifer tests, yield from each well is assumed to be
approximately 2 gpm. Approximately 83,520 gallons per day of extracted groundwater would be
pumped to the NRWWTP for treatment. The design, construction, start-up, and
decommissioning costs of this alternative would be $2,391,920. Operation and maintenance
costs, including treating the extracted water, would cost approximately $4,206,240 over 30 years.
The present worth of the costs associated with the extraction process is $4,012,835.
Monitoring. ENSR assumed that 10 monitoring wells (MW-105, MW-108, MW-109, M W-110,
MW-111, MW-112, MW-117, MW-118, MW-119, and MW-120) and 2 surface water locations
(SW-20 AND SW-22) would be sampled triennially and analyzed for nitrate for the life of the
project, in addition to the monitoring wells that are monitored triennially for the land application
permit. In addition, the 29 extraction wells would be sampled and analyzed for nitrates annually
for the life of the project. Groundwater data from these extraction wells, monitoring wells, and
surface water samples would be used to monitor the performance of this alternative. It should be
noted that CORPUD already samples the compliance wells three times a year as part of the
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compliance monitoring (for the biosolids application permit) for the Site. Analytical data from
these test wells would be used to evaluate the effectiveness of this alternative. For the purpose of
costing and comparison, it was assumed that the project life of this alternative is 30 years. The
costs to monitor compliance wells (test wells) required under the biosolids permit are not
included in this estimate. The cost of monitoring over 30 years would be approximately
$2,307,600, with a present worth of $1,046,665.
3.6. Financial Hardship and Lack of Public Benefit
The full-compliance alternative would create a serious financial hardship on CORPUD requiring
that it spend approximately $70 million dollars beyond the approximate $9 million that it will
have to spend to implement its preferred alternative. Further, the immense expenditure required
to implement the full compliance alternative would not result in commensurate public benefit
relative to the more cost-effective and fully protective proposed remedy.
To illustrate the financial hardship that the full compliance alternative would incur, the City has
provided its projected operating and capital budgets in Table 8. The operations budget for the
NRWWTP and associated spray irrigation is approximately $14,000,000 per year over the next
few years. Operations and maintenance costs for Alternative 1 would be over $5,000,000 during
the first 3 years of the project. The combined capital, operation, and maintenance costs accounts
for almost a third of CORPUD's expected total annual operations budget over the next few years.
When the denitrification system is discontinued in the third year of the project, the annual
operations and maintenance costs decrease to approximately $1,000,000. However, this is still a
significant annual cost accounting for about seven percent of the operations budget.
The projected capital costs (including design, construction and startup) of Alternative 1 are
predicted to be $35,402,500 which would have to be paid out by the City over the first 2 years of
CAP implementation. Because of the age of the facility and the need for expansion to keep up
with the growing population, the NRWWTP requires a number of expensive improvements over
the next several years. Over the next three years when the capital costs of the CAP are likely to
be incurred by CORPUD, the CORPUD's capital budget for the NRWWTP for fiscal year 2006-
07 is $58,175,000, for 2007-08 is $31,625,000, and for 2008-2009 is $19,800,000. Assuming
that the City would spend more than $17,500,000 per year for the first two years of the project,
this sum would be approximately 30 to 90 percent of its total capital budget in any of the next
few years. The City would be compelled to divert funds allocated to the numerous and extensive
capital improvements planned for the NR WWTP putting the protection of water quality and the
availability of high quality wastewater treatment service to the area's growing population at risk.
This would be a great detriment to public health and outweigh any benefits of Alternative 1.
Further, the full-compliance alternative requires the expenditure of $79 million dollars to clean
up groundwater that has a very low likelihood of actually being used by the public for drinking
water or any other purpose.
Finally, Alternative 1 would have detrimental effects on the environment as the remedy is very
invasive, requiring the installation of 426 pumping wells, each installed at 100-foot intervals,
along portions of the City's property boundary where groundwater exceeds or is expected to
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exceed· the nitrate groundwater standard. This hydraulic barrier would result in reducing
groundwater discharge and thus stream baseflow to several streams in the area, particularly
Beddingfield Creek. This reduced flow would be potentially detrimental to the ecology of those
streams.
On potential benefit of Alternative 1 is that it accelerates the time by which off-site groundwater
in the downgradient areas could be used for human consumption if needed. However, there is no
net public benefit in spending an extra $70 million to accelerate the cleanup of groundwater in
area where there is little or no need to use the groundwater for human consumption. While it is
desirable that the groundwater eventually be remediated to unrestricted use standards, the
additional time required to achieve that goal utilizing CORPUD's preferred remedial alternative
will not endanger public health because no one is using or can use any contaminated
groundwater as a water supply.
3.7. Information Regarding Adjacent Property Owners
CORPUD obtained the names and address of those owning property within the proposed
variance area as well as property owners adjacent to the site covered by the variance from the
Wake County Geographic Information System. A list of these names and addresses are provided
in Exhibit 3.
4.0 Summary and Conclusions
The nitrate contamination at the site does not and will not endanger public health or the
environment provided that (i) contaminated groundwater is not used for human consumption,
and (ii) the impacts of nitrogen loading to the nutrient-sensitive Neuse River are offset.
CORPUD has provided city water service to all properties in the area where there was any risk
from using groundwater as a water supply.
CORPUD does not believe the alternative that would fully comply with the EMC's rules is
economically reasonable. It would cost in excess of$79,000,000 to remediate all areas where
the groundwater standard has been exceeded by installing and operating extraction wells around
the entire compliance boundary and implementing enhanced denitrification in area where nitrate
contamination has already migrated beyond the compliance boundary. Although the proposed
installation of a limited number of extraction wells is not strictly needed to protect public health
and the environment, it does provide a measure of additional benefit (by accelerating the time by
which off-site groundwater in the downgradient area could be used for human consumption if
needed) at a much more reasonable and manageable cost ($9,000,000). The full compliance
alternative would create a financial hardship on CORPUD and in particular would divert needed
funds from the numerous and extensive capital improvements planned for the NRWWTP in the
near future to ensure the protection of water quality and the availability of high quality
wastewater treatment service to the area's growing population. Nor would the immense
expenditure required to implement the full compliance alternative result in commensurate public
benefit relative to the more cost effective and fully protective proposed remedy. Moreover, the
full compliance alternative would result in reducing groundwater discharge and thus stream
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baseflow to several streams in the area, particularly Beddingfield Creek, which would be
potentially detrimental to the ecology of those streams.
5.0 References
ENSR, 2002, Comprehensive Site Assessment, City of Raleigh, Neuse River Waste Water
Treatment Plant, December.
ENSR, 2003, Supplemental Site Assessment, City of Raleigh, Neuse River Waste Water
Treatment Plant, December.
ENSR, 2005, Revised Corrective Action Plan, City of Raleigh, Neuse River Waste Water
Treatment Plant, December.
42299&0 .6
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