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^ A R C A D I S Infrastructure, environment, buildings Imagine the result

DISCHARGE ALTERNATIVES REPORT

Public Well TCE Site (DE-1361) Millsboro, Delaware

January 14, 2011

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Chase McLaughlin Staff Engineer

inKLenzo Frai Project Director, Vice President

£o&.

^ U Darren Scillieri Project Manager

Discharge Alternatives Report

Public Well TCE Site (DE-1361), Millsboro, Delaware

Proparod lor

United Stales Environmental Protection Agency

Region lit

PropaiQd by.

ARCADIS U.S., Inc.

10 Friends Lane

Suite 200

Newtown

Pennsykania 18940

Tel 267.685.1800

Fax 267.685.1801

On behalf of

tulerck and Co., Inc. (Merck) and

Mallinckrodt Veterinary, Inc (Mallinckrodt)

Qui Re(.:

NP000686.0001.00005

Dato:

January 14, 2011

This docurriBnt is intended only for the use

of the individual or entity for which it was

prepared and may contain informafion that

is privileged, conlidenlial and exempt from

disclosure under applicable law. Any

dissemination, distribution or copying of

this document is strictly prohibited.

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(^ARCADIS Table of Contents

1. introduction

1.1 Purpose and Objectives

1.2 Report Organization

2. Site Setting

2.1 Site Physical Setting

2.2 Site Geology

2.3 Site Hydrogeology

3. Public Wells 1 and 2: System Description and Operations

3.1 Public Wells 1 and 2 System Configuration

3.2 PW-1 and PW-2 Influent/Effluent Water Quality

4. Regulatory Obligations and Permitting Requirements

5. Discharge Alternatives Evaluation

5.1 Identification of Discharge Alternatives

5.2 Alternative 1 - Groundwater Reinjection

5.3 Alternative 2 - Spray Irrigation

5.4 Alternative 3 - Surface Water Discharge to Millsboro Pond

5.5 Comparative Evaluation of Alternatives

Conclusions

References

1

1

2

3

3

3

4

5

5

6

7

7

8

11

12

13

15

15

Tables

Table 1

Table 2

Table 3

PW-1 2010 Monthly Operational Data

PW-2 2010 Monthly Operational Data

2010 Trichloroethene Analytical Results

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_ Table of Contents (SI ARCADIS

Table 4 Anion Analytical Results

Table 5 Altemative Discharge Saeening Summary

Figures

Figure 1 Existing Monitoring Well Locations

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Public Well TCE Site (DE-1361), IVIillsboro, Delaware

1. Introduction

1.1 Purpose and Objectives

This Discharge Altemative Report (DAR) has been prepared by ARCADIS U.S., Inc. (ARCADIS)

on behalf of Merck and Co., Inc. (Merck) and Mallinckrodt Veterinary, Inc (Mallinckrodt), to

evaluate altemative discharge options for groundwater treated for trichloroethene (TCE) from

Millsboro Public Wells 1 and 2 (PW-1 and PW-2). This document responds to the United States

Environmental Protection Agency (EPA) November 26, 2010, Amendment Number 1 to the

Administrative Settlement and Order on Consent dated May 11, 2010 (Amendment No. 1).

Amendment No. 1 requires submittal of a report assessing certain alternatives available for

treated groundwater discharge from PW-1 and PW-2 other than use as part of the Town of

Millsboro's water supply. The goal of this DAR is to recommend an appropriate alternative for

the treated effluent discharge from PW-1 and PW-2 for implementation as soon as practicable.

PW-1 and PW-2 are groundwater extraction wells that presently provide hydraulic control of

TCE-impacted groundwater in the Columbia aquifer. Amendment No. 1 requires that the

evaluation of the discharge options address the following: (i) the expeditious disconnection of

Public Wells 1 and 2 from the Town of Millsboro water supply; (ii) the continuation of

pumping of such wells at their maximum capacity or in such lesser amount sufficient to

maintain hydraulic control of TCE in the subsurface groundwater; and (ill) the discharge or

disposal of water produced by such pumps in a manner that will not cause further harm to the

environment or negate the beneficial effects of the continued pumping of such wells.

Cun^ently water pumped from PW-1 and PW-2 is treated through dedicated granular activated

carbon (GAC) systems located proximal to each vjeW. To date, the treated effluent from PW-1

and PW-2 has discharged to the town water supply; however, the installation and start-up of a

new Manokin Aquifer pumping well (PW-5) and a new water treatment plant has reduced the

operational uptime of PW-1 and PW-2. This supplemental supply has resulted in a reduced

output from PW-1 and PW-2 since August 2010 (the average flow rate is approximately 30 to 50

gpm, See Tables 1 and 2). The results of the hydrogeologic study and the numerical flow

simulations presented during the August 3, 2010 meeting at the Town of Millsboro indicate that a

significant reduction in pumping of the Columbia Aquifer risks a loss of the lateral and vertical

migration control established under the past pumping conditions. Therefore, it is imperative that

an altemative discharge option be implemented as soon as practicable to allow sustained higher

withdravral of water from PW-1 and PW-2 to minimize the potential for migration of the TCE

plume both laterally and vertically.

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The following list represents altemative discharge options for PW-1 and PW-2 to be considered

as specified in the Amendment No.1:

• Discharge of said water to Millsboro Pond or Indian River Bay;

• Reinjection of said water into a local aquifer; and

• A spray irrigation and/or rapid infiltration system.

Accordingly, the following discharge alternatives were evaluated:

• Reinjection into the Columbia Aquifer in the WB Atkins Memorial Park; use of an existing

18-inch benefiaal reuse water line, and altemative constnjction of a 6-inch line to deliver

water to the new injection wells were each considered,

• Spray irrigation via beneficial reuse water line to be completed in the future as part of

existing Town of Millsboro construction plans, and

• Surface water discharge to Millsboro Pond via a new 6-inch high density polyethylene

(HDPE) pipeline from the PW-1 and PW-2 systems to the pond.

The primary objective of the DAR is to recommend the altemative that will allow for the most

rapid implementation to resume proper operation of PW-1 and PW-2 and provide containment of

the TCE plume.

1.2 Report Organization

The report is organized as follows:

• Section 2 presents background information concerning the site physical and

hydrogeologic setting;

• Section 3 describes the PW-1 and PW-2 system characteristics;

• Section 4 describes the regulatory obligations and permitting requirements;

• Section 5 reviews the discharge altematives, and evaluates the feasibility of each

altemative;

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• Section 6 provides the DAR's conclusions; and

• Section 7 provides a list of references

2. Site Setting

2.1 Site Physical Setting

The Town of Millsboro well field is situated approximately 1,500 ft dowmgradient from the

Millsboro TCE site. See Figure 1. On-going environmental investigations indicate that affected

groundwater has migrated laterally in the shallow portion of the groundwater system (less than

60 feet deep) resulting in a narrow TCE plume. In the vicinity of the Millsboro well field, the

impacted groundwater has been drawm deeper and resulted in impacts above the TCE maximum

contaminant level (MCL) in two of Millsboro's water supply production wells ( PW-1 and PW-2).

Three additional production wells (PW-3, PW-4, and PW-5) have been installed deeper in the

system. Based on the available data, the deeper wells have not indicated site-related impacts

above the TCE MCL to date.

2.2 Site Geology

Based on site-specific boring logs and regional information, the subsurface geology is principally

composed of the following hydrostratigraphic units:

• Omar Formation and Beaverdam Formation of Columbia Group (from ground surface to approximately 95 feet deep) (DGS, 1984, 1990)

• The Bethany Formation (from approximately 95 to 180 feet deep) is composed of muddy silt beds overiying sands and sandy mud deposits wrfiich act as a semi-confining unit for the lower aquifers (DGS, 2004)

• The Pokomoke, Ocean City and Manokin Aquifer system (from approximately 180 to 260 feet deep); and

• The St. Marys formation (a gradational transition to underiying clay and sand units w/hich compose the bottom of the Manokin aquifer).

The Town of Millsboro well field is located on the Atlantic Coastal Plain and is underiain by the

Columbia Formation (Pleistocene in age). The Columbia Formation is described by the

Delaware Geological Survey (DGS) as yellow to reddish-brown, fine to coarse feldspathic quartz

sand with varying amounts of gravel. Scattered beds of tan to reddish-gray clayey silt are

common. In places, the upper 5 to 25 feet consists of grayish- to reddish-browm silt to very fine

sand overlying medium to coarse sand. Near the base, clasts of cobble to small boulder size

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have been found in a gravel bed ranging from a few inches to three feet thick. The Columbia

Fomiation fills a topographically irregular surface, can be up to 100 feet thick, and is interpreted

to be a body of fluvial glacial outwash sediment. Geologic findings from previous investigations

conducted at the Site are consistent with the DGS's description of the Columbia Fonmation.

The Columbia Formation is underiain by the Bethany Formation. Based on the production well

drilling logs from Millsboro, the Bethany Fonnation has been characterized as "gray clay wth

sand near its top" and "silt to gray silty-sand wnth increasing clay content" near its bottom. Given

the proximity of the well field to the Atlantic shore, significant variability in sand and day content

is expected both laterally and vertically, as the sediments transition ft'om high- to low-energy with

the historical sea level rise and fall. Qualitatively, the site's depositional setting and observed

lithology are consistent with a leaky aquifer, or low-yield aquifer, instead of a competent aquitard.

The Manokin Formation underiies the Bethany at approximately 180 feet below grade. The

Manokin Formation is characterized as fine to medium and coarse gray sand.

2.3 Site Hydrogeology

Ground surface elevations (i.e., topography) at the Site range from approximately 20 ft to 25 ft

above Mean Sea Level (MSL). Groundwater monitoring results from 2009 indicate that

groundwater elevations at the Site range from approximately 5 ft to approximately 15 ft MSL.

Horizontal groundwater flow mimics the local topography and generally flows north-east towards

the Indian River and Millsboro Pond. Regional gradients are approximately 1.05 X 10E-4 ft/ft and

6.31 X 10E-4 ft/ft in the unconfined and confined aquifers, respectively (DGS, 1984). Average

yeariy precipitation and evapotranspiration at the Site are approximately 40 inches and 25

inches, respectively (ESC, 1990).

Millsboro Pond and the Indian Bay Inlet are the closest surface water bodies and are located

approximately 1,200 ft downgradient of the Towm of Millsboro well field. The Indian Bay Inlet

exhibits tidal fluctuafions wrfiereas the section to the west that is dammed (Millsboro Pond) does

not exhibit tidal fluctuations.

Migration of the plume ft^om the Millsboro TCE site is influenced by the nature and stnjcture of

the sediments comprising the aquifer systems beneath the town and pumping in the Millsboro

well field.

Regional water production and local testing results indicate that the Columbia and Pokomoke,

Ocean City, and Manokin (Manokin) Aquifers are capable of producing significant water yields.

However, serious doubt exists regarding the Bethany Formation as a competent aquitard, and its

ability to prevent downward migration of impacted water from the Columbia, particulariy vrfien

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Millsboro's deep wells are all operating. The available data suggests that the nature of the

Bethany fonnation leads to its classificafion as a leaky aquitard (DGS, 2004) and in some areas

along the mid-Atlantic coast is transmissive enough to be exploited for water supply.

Regional data indicate that recharge of the Columbia and Manokin Aquifer systems is primarily

through infiltration of rainwater, and most of the recharge to the Manokin aquifer probably occurs

in the outcrop area. This result implies that a significant portion of water removed via pumping in

the deeper Manokin fomnation would be replaced by water derived from geologic formafions

above it.

3. Public Wells 1 and 2: System Description and Operations

3.1 Public Wells 1 and 2 System Configuration

Public Wells 1 and 2 each have independent treatment systems utilizing liquid phase granular

activated cart)on (LPGAC) to remove TCE. Each well has a 20 horsepower (HP) submersible

pump that pumps groundwater from the Columbia Aquifer through three parallel pairs of LPGAC

vessels operating in series. The three lead vessels in each pair provide primary treatment for

TCE; the lag vessels in each of the three pairs act as a polishing step to adsorb TCE that may

escape from the primary unit. The midpoint concentration is monitored to determine the need for

change outs.

The piping network between each wellhead and the vessels consist of 3-inch steel that

transitions to schedule 80 polyvinyl chloride (sch. 80 PVC) piping prior to a flanged connection to

a 3-inch flow meter. Following the flow meter, the PVC line manifolds to 3 lines with a ball valve

for each lead vessel. Each ball valve in the manifold is fitted wth a male cam-lock connection so

system piping can be transitioned for lead/lag operation follown'ng a LPGAC change out. The

effluent piping of each vessel has a ball valve and cam-lock connection for lead/lag piping

variations. The lag vessel piping manifolds to the system effluent that distributes either directly to

the tovm supply or to storage tanks depending on the demand.

In June of 2010, mechanical upgrades were conducted to install air relief valves to the top of

each vessel to prevent air entrainment w/hich can lead to channeling and eariy breakthrough.

Future system upgrades will be conducted followflng the altemative discharge design to

inconporate alarnis that wnll notify personnel of system shutdowns. These upgrades wnll help to

minimize downtime and target maximum uptime to maintain plume capture.

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3.2 PW-1 and PW-2 Influent/Effluent Water Quality

Table 3 provides a summary of weekly PW-1 and PW-2 system influent, midpoint, and effluent

discharge water quality sample results, for the period from January 2010 to December 2010.

TCE concentrations have fluctuated for PW-1 and PW-2 with the decreased pumping rates. PW-

1 has had a maximum concentration of 820 pg/L (ppb) and PW-2 concentrations have dropped

to less than 10 ppb since well output was reduced in August 2010.

Midpoint and effluent concentrations are monitored to schedule change outs. Typically a change

out is scheduled if midpoint TCE concentrations are between 2-3 ppb or above 5 ppb. If

concentrations are noted in the effluent from the second unit, the systems are immediately

shutdown and change out is immediately scheduled.

Samples were collected from PW-1 in October and from PW-1 and PW-2 in December 2010 to

analyze nitrate and other anion levels. Nitrate concentrations ranged from 6.0 to 7-0 mg/L. These

results are consistent wflth nitrate concentrations observed in samples collected by the Tovm of

Millsboro. Analytical results for nitrate, bicarbonate, cart)onate, chloride, and sulfate are

presented in Table 4.

4. Regulatory Obligations and Permitting Requirements

The three discharge altemative opfions of the treated effluent groundwater, the associated

pemiitting requirements, estimated time to receive permit approval, and the relevant pemiitting

authority are presented below:

Discharge Option

1. Reinjection to the Columbia aquifer in the WB Atkins Memorial Pari<

Permit Required

Underground Injection Control Pennit

Estimated Time to Pennit Approval

60 - 90 days (includes public notice and comment period)

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2. Spray imgation

via beneficial reuse'

water line to be

. completed in the

future as part of

existing Town of

Millsboro

construction plans.

3. Surface water

discharge to

Millsboro Pond

Land Application

Permit

NPDES permit

105-135 days

(includes 60 - 90 day

review of the Design

Report, 30 day review

of the plans and

specifications, and a

15-day public notice

and comment period)

60 - 90 days

(includes public

notice and

comment period)

5. Discharge Alternatives Evaluation

5.1 Identification of Discharge Alternatives

This section identifies and describes the potential discharge alternatives for PW-1 and PW-2

water that are currently under consideration. Each altemative will require that backflow

preventers be placed on both the PW-1 and PW-2 discharges before manifolding together into

one 6-inch HDPE line that mns north to Church Street for the future altemative connection. The

existing piping from each system WAII remain in case the Tow/n water supply needs to be

supplemented by either treatment system. These wells would need to be identified for this

application on the subsequent water allocations pennit. The ability to discharge to the Town

water supply will be coordinated wnth Millsboro and designed into the system.

This DAR evaluated the followflng three altematives:

1. Reinjection into one or more wells in the WB Atkins Memorial Park;

2. Spray irrigation/beneficial reuse; and

3. Surface water discharge to Millsboro Pond by installation of a 6-inch high density

polyethylene (HDPE) pipeline from the pumping systems to the pond.

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A detailed analysis of each of the alternatives is provided in the following sections. Detailed

analysis performed for the altematives consist of an assessment against each of the following

evaluation criteria:

1. Overall protection of human health and the environment;

2. effectiveness;

3. implementability;

4. state/community concerns; and

5. cost-effectiveness.

This DAR does not fully evaluate system design. Design and final costing will be conducted

following selection and regulatory approval of a discharge altemative.

5.2 Alternative 1 - Groundwater Reinjection

This altemative focuses on pumping groundwater from the Columbia aquifer, treating for TCE,

and then injecting via injection wells located in WB Atkins Memorial Park back into the Columbia

aquifer. Treated water is transported to the injection wells via the existing 18-inch beneficial

reuse line that runs west down Church Street before fuming north on Sussex Street and then

tuming west into the park. A valved connection would be tapped into the existing beneficial

reuse line piping and 6-inch HDPE weuld run from the connection to the new injection wells. The

well design w/ill depend on the volume that can be discharged based on the subsurface

characteristics at the Site. Presence of high permeability media and high aquifer recharge are

necessary for using this discharge option. The injection can be conducted under gravity or

pressurized through horizontal or vertical wells. Beyond the benefit of disposal of the treated

water, there are two primary advantages to recharging the aquifer :(1) beneficial reuse

of treated groundwater through aquifer recharge, and (2) preventing acute deterioration of

the groundwater yield of the aquifer.

OverafJ Protect/on of Human Health and the En wronment -This altemative provides a level

of protection similar to that of the cun-ent system operation. PW-1 and PW-2 treatment systems

wflll provide hydraulic control which is still the primary objective, wflth the only difference being on-

site injection instead of potable water use of treated groundwater. Detailed hydraulic modeling

suggests that re-injection can be accomplished wflthout compromising the ability of PW-1 and

PW-2 to maintain hydraulic control. (See the Executive Summary of Hydrogeologic Investigation

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of the Downward Migration Potential of Dissolved Solutes Present in the Columbia Aquifer to

Reach the Manokin Aquifer [ARCADIS, October 2010]). Addifional detailed modeling will be

required to determine the appropriate design and location of the reinjection wells. In addifion,

there is no deleterious impact on the aquifer water quality in the area of recharge since water of

similar quality, from the Columbia formation neartsy (treated for TCE), is being recharged.

This alternative w/ill not affect protection of human health and the environment. Treated water

from the systems discharge is anticipated to have similar nitrate concentrations to the

groundwater in the reinjection zones.

Effectiveness — In general, the Columbia aquifer is very penneable and the results of

preliminary hydraulic modeling suggests infiltrafion via reinjection wnll be effective. Aquifer •

recharge testing would be required to determine the location for effective recharge of

groundwater.

Implementability—An Underground Injection Control (UIC) permit may be required for

implementation of this option. The required equipment and services for constructing and

operating injection wells are available. The potential to use the existing beneficial reuse line

makes this option the fastest possible to install. The injection wells and short distance of piping

can be installed wflthin a matter of 3 to 6 months.

Implementafion will require tapping into the existing infrastructure for the beneficial reuse line.

New piping wnll be installed from the beneficial reuse line to the injection wells and the wells will

be protected by vaults surrounded by bollards. Engineering design work, materials procurement,

equipment and electrical components installation, as well as system construction and testing will

also be required.

If the current discharge line is not available for use in the reinjection system, implementation of

this altemative WAII require new piping to be installed ft^om the current system locations to the

proposed injection wells. Construction would include wori< within local side streets (Church and

Sussex Streets) to extend the piping to WB Atkins Memorial Pari<. The installation of the

conveyance piping through Church Street and Sussex Street may require building and road

closure permits.

Sctiedule/Estimated Timeline—Since most of the infrastructure is already installed this

altemative would be the most time efficient selecfion. Construction activities for well installation

and piping connecfions are anticipated to take 3-6 months if the beneficial reuse line is used.

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If a new discharge line is required, construction activities to permit and install new piping

between the wells and the treatment systems wnll increase the timeline for implementation.

Construction activities for well installation and installation of new piping are anticipated to take 9-

12 months.

State/Community Concerns - The reintroduction of treated groundwater back into the

Columbia Aquifer should not be a concern because TCE will have been removed.

The treated Columbia fonnation water will be reinjected back into the Columbia aquifer

in a slightly different location in essentially the same condition it was removed - except

for the treatment of TCE.

Cost— The capital costs associated wflth implementing this option are expected to be moderate

to high based on the number of injection wells required. O&M costs associated wnth the

maintenance of the discharge line are expected to be moderate to high depending on the degree

• of scaling and fouling encountered wnthin the discharge piping and injection wells. If fouling is

excessive a backup reinjection well may be required to accommodate maintenance of the

primary wells.

The estimated costs are provided in the Alternative Discharge Saeening Summary table

attached as Table 5. These costs include capital costs associated wflth construction of

reinjection systems and yeariy costs for routine treatment system O&M including groundwater

monitoring costs. Anticipated O&M activities associated with the reinjection system include daily

operation of the extraction, treatment and reinjection systems, equipment repairs and

preventative maintenance activities, operational and compliance monitoring activities, purchase

and installation of supplies, property maintenance, waste management, and well redevelopment

activities.

Estimated capital costs for construction of inft-astructure piping and reinjection wells are

approximately $450,000, including contingencies. Conceptual constnjction costs include the

installation of backflow preventers, vaults, conveyance piping, controls, plus the installation of an

estimated two 90-foot-deep injection wells and associated piping.

If the current discharge line is not available to facilitate delivery of the treated groundwater to the

injection well locations the addition of new HDPE piping and valves between the treatment

systems and the wells WAH be required. Constnjction vAW likely require permits and road closures.

Estimated capital costs for construction of the new discharge piping are approximately $150,000.

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5.3 Alternative2-Spray Irrigation

This altemative would utilize the existing beneflcial reuse wateriine that currently njns from the

treatment system area to WB Atkins Memorial Park; however, it is not anticipated that the line WAII

be completely installed and ready for at least two to three more years. When complete the

beneficial reuse pipeline will run approximately 2 to 3 miles northwest to a storage tank that will

distribute water for irrigation.

Overall Protection of Human Health and the Environment- If operated year-round, this

altemative could provide a level of protection similar to that of the current system operation. PW-

i and PW-2 treatment systems wnll provide hydraulic control w/hich is still the primary objective.

This alternative will not affect protection of human health and the environment.

Effectiveness— Spray irrigation would be an alternative use of treated groundwater from PW-1

and PW-2. However, this option vj\\\ not provide the year round discharge and disposal of the

effluerit from PW-1 and PW-2 required to maintain plume control.

Implementability — The Towm of Millsboro is cun^ently pursuing installation of a beneficial reuse

line for the purpose of spray imgation. Beneficial reuse for spray irrigation w/ill not be a possibility

for potentially 2 to 3 more years wtiile infrastructure is installed to carry the pipeline to the final

end use location. Even when the pipeline is installed and water is sent to the imgation tanks for

reuse, this option will require another end use of the treated water from PW-1 and PW-2 during

times of decreased demand for irrigation water. At present, end uses sufficient to consume all

effluent from PW-1 and PW-2 have not been idenfified. Penmitting is also difficult and is likely

to.push back the construction of the pipeline.

Schedule/Estimated Timeline— Per conversations with Town officials construction activities for

additional beneficial reuse piping WAII not be completed for an estimated 2-3 years.

State/Community Concerns - Discharge of treated groundwater via spray imgation for

beneficial reuse should not be a concem. Delaware has a long history of promoting beneficial

reuse of reclaimed water. Some fields in Delaware have been receiving reclaimed water since

the 1970's Wflth no adverse effects to the fields, crop yields or the water table beneath the field.

As of 2002, there are 23 facilities permitted in Delaware to apply reclaimed water onto 2200

acres of land. Most of the land used for beneficial reuse is agricultural, but reclaimed water is

also used to irrigate tvro golf courses and several tracts of wooded land.

Cost—The capital costs associated wnth implementing this option are low. Existing/future lines

would be utilized to convey treated system water.

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5.4 Alternative 3 - Surface Water Discharge to Millsboro Pond

Local surface water bodies may be available to accept discharge ft"om a groundwater treatment

system. Millsboro Pond is located approximately 1,200 fl north of the Millsboro water plant.

Smaller tributaries and stonm drains are closer and discharge to the Millsboro Pond. A discharge

line and an outfall can be constnjcted from the treatment system to existing drainage toward

neart)y surface water bodies.

Overall Protection of Human Health and the Environment - This altemative provides a level

of protection similar to that of the past system operation. PW-1 and PW-2 treatment systems vAW

provide hydraulic control which is still the primary objective.

Nutrient loadings have been idenfified as a significant contribution to the degradation of

Delaware's surface waters. DNREC enforces regulations governing the pollution control strategy

for the Indian River and Bay, Rehoboth Bay and Little Assawoman Bay Watersheds. The

Pollution Control Strategy is designed to reduce the amounts of nitrogen and phosphoms

entering the Inland Bays and their tributaries to levels required to meet water quality standards.

The strategy includes provisions to establish buffers to filter and remove pollutants before they

flow into the Inland Bays and their tributaries

This altemative w/ill not affect protection of human health and the environment. However,

treatment for nitrates will likely be required before discharging to surface water.

Effectiveness groundwater.

-Surface water discharge is an effective disposal method for treated

Implementability — A discharge permit and monitoring will be required. An environmental

assessment of the impact on the discharge may be required. Nitrate treatment will more than

likely be required. Infrastmcture piping and constmction logistics through existing town roads are

very invasive. There are no clear paths to Millsboro Pond that don't require going through private

property or busy streets.

The cun-ent nitrate concentrations measured in October and December 2010 in PW-1 and PW-2

were between 6 to 7 mg/L; these levels are attributable to background. See Table 4. Nitrate

treatment WAII require ion exchange for direct surface water discharge to Millsboro Pond. The

system effluent streams would be combined prior to ion exchange treatment. Two

vessels would be operated in series to remove anions from the combined streams.

The treated effluent will then discharge to conveyance piping to the Millsboro Pond.

Nitrate treatment w t̂h ion exchange wn'th cun-ent site concentrations of 6-7 mg/L will require

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frequent resin change outs or regeneration that will cause system dovmtime and generation of

residual waste from the change-out or regeneration process.

Ion exchange technology is effective for removing nitrate; however, the capital and O&M costs

associated with ion exchange technology are extremely high. The frequency of resin change

outs (or regeneration) makes ion exchange an extraordinary logistic burden because vendor-

provided resin usage rates suggest a change out (or regeneration) frequency of every 1 to 2

weeks.

Schedule/Estimated Timeline— Constmction activities to permit and install the new piping

between the surface water discharge and the treatment systems is considered to be complex as

the piping w/ill probably have to be routed up main roads through the Tovm of Millsboro. Design

and constnjction activities for surface water outfall and installation of new piping and nitrate

treatment system are anticipated to take 1-2 years. Furthermore, O&M associated wflth frequent

resin change outs activities would lead to system dovmtime.

State/Community Concerns - Discharge of treated groundwater via surface discharge should

not be a concem as the effluent discharged meets drinking water quality standards.

Cost— Capital costs will be very high based on the distance and the impact to private property

and/or road closures. Capital costs are anticipated around $600,000 to run conveyance

piping to Millsboro Pond and install an outfall structure. Nitrate treatment requirements add

$1,100,000 to the capital costs and $600,000 for the annual O&M costs, an order of magnitude

higher than other options. Accordingly, implementation of any discharge option involving

treatment of nitrates is time and cost prohibitive.

5.5 Comparative Evaluation of Alternatives

This section compares the altematives, utilizing the criteria evaluated in the above sections. The

inifial evaluafion includes a comparison of the altematives against the threshold criteria. The

threshold criteria represent the minimum requirements for each alternative in order to be eligible

for selection. The primary balandng criteria (protection of human health and the environment,

effectiveness, implementability. State and community concems, and cost-effectiveness) allow.for

the direct comparison of altematives against each other.

Overall Protection of Human Health and the Environment

All discharge altematives would allow for the system to operate and maintain containment of the

groundwater plume preventing the potential of constituent transport. With system downtime

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^ ARCADIS



being the most critical component of this evaluation, Altemative 1 will be the fastest opfion to

implement.

Effectiveness

Altemafive 1 (Reinjecfion using the exisfing beneficial reuse line) is considered an effecfive

discharge altemative. Reinjection of the groundwater wnll allow the systems to run and maintain

hydraulic control of the groundwater plume. Altemative 2 (Spray Imgation) is not a satisfactory

alternative because it WAII only provide a complete discharge altemafive during periods of high

imgation demand. Alternative 3 is not a satisfactory altemative because of excessive time and

cost constraints along with the uncertainty associated vflth the placement of the discharge line

through private properties.

Implementabilitv

Altemafive 1 is easily implementable and has the best potenfial for an expedited implementation.

Injection wells WAII be installed in WB Atkins Memorial Park and piping connections could be

tapped into the existing beneficial reuse line. While Altematives 2 and 3 are implementable, it

\N\\\ simply require a longer fimeline to acquire road closure permits and install the piping.

Permitting risks for each of these altematives are the same.

State/Community Concems

Although none of the altematives are likely to cause public concern. Alternative 1 does not

involve discharge to a surface water body, and WAII most likely meet wflth public acceptance.

Cost-Effectiveness

Capital and O&M costs would be associated with all three discharge altematives. Based on

preliminary cost estimates developed for this report (Table 5), Altemative 2 would involve low

upfront capital costs however, it will not be an implementable solution for 2-3 years. Capital costs

associated wnth Altemative 3, the surface water discharge option, would be very high based on

the distance and the impact to private property and/or road closures. In addition, this discharge

option would include an extraordinarily high O&M cost associated with nitrate treatment - making

this option cost prohibitive. Altemative 1 would be the least expensive opfion for the fastest

installation, requiring approximately $450,000 of capital, wnth estimated annual OM&M costs of

about $25,000.

14

AR000456

^ A R C A D I S



6. Conclusions

This DAR has evaluated three possible altematives:

• Reinjecfion into two wells in the WB Atkins Memorial Pari< utilizing either the exisfing 18-

inch beneficial reuse wateriine or a new 6-inch HDPE pipeline.

• Spray irrigation/beneficial reuse.

• Surface Water Discharge

Altemafive 1, reinjection into wells in the WB Atkins Memorial Park ufilizing exisfing 18-inch

beneficial reuse wateriine, has been detemiined to be the most rapidly implementable of the

altematives. With system dovmtime being the most critical component of this evaluation.

Alternative 1 will be the fastest option to implement. Altematives 2 and 3 would require a longer

design and construction/installation timeline for conveyance piping networks.

Spray Irrigation (Altemative 2) is not considered a viable discharge option due to time-frame

required for full implementation and its inability to assure year round disposal. Surface water

discharge (Altemative 3) is not considered due to low implementability, high costs, extended

timeframes, and the requirement of nitrate treatment.

Regardless of the altemative implemented, the PW-1 and PW-2 systems will be retrofitted wnth a

backfiow preventer so flow can be directed to the town water supply or to the discharge

altemative so the Town wnll not lose PW-1 and PW-2 capacity for emergency situations.

7. References

ARCADIS US, INC., 2010. Evaluation of Potential Risks Associated with Expanded Pumping in

IVIanokin Aquifer, Millsboro, Delaware.

Delaware Geological Survey (DGS), 1984. Hydrology of the Manokin, Ocean City, and

Pocomoke Aquifers of Southeastern Delaware, Report of Investigation No.38

Delaware Geological Sun/ey (DGS), 1990. Ages of Bethany, Beaydam, and Omar Formations of

Southern Delaware, Report of Investigation No.47

15

AR000457


( ^ ARCADIS

Millsboro, Delaware

Delaware Geological Survey (DGS), 2004. The Cat Hill Formation and Bethany Fonnation of-

Delaware, Report of Invesfigation No.67

EPA, 2010. Amendment Number 1 to Administrative Settlement and Order on Consent for

Removal Action Response. November 2010

16

AR000458

ARCADIS

Table 1 PW-1 2010 Monthly Operational Data Millsboro, Delaware

PW-1

Date

Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10

Flow Differential

(gal)

5,050,400 4,318,500 4,778,100 5,529,000 6,774,100 7,803,500 8,041,800 4,297,501 1,455,901 2,345,700 1,236,600 717,900

Time Differential

(days)

31 28 31 30 31 30 31 31 30 31 30 31

Time Differential

(min)

44,640 40,320 44,640 43,200 44,640 43,200 44,640 44,640 43,200 44,640 43,200 44,640

Up Time (gal/200)

(min)

25,252 21,593 23,891 27,645 33,871 39,018 40,209 21,488 7,280

11,729 6,183 3,590

Up Time

(days)

17.5 15.0 16.6 19.2 23.5 27.1 27.9 14.9 5.1 8.1 4.3 2.5

Up Time

%

57% 54% 54% 64% 76% 90% 90% 48% 17% 26% 14% 8%

Average Flow (gpm)

113 107 107 128 152 181 180 96 34 53 29 16

Notes: gal: gallons gpm: gallons per minute PW-1 has an approximate fiowrate of 200 gpm

Page 1 of 1

AR000459

ARCADIS

Table 2 PW-2 2010 Monthly Operational Data Millsboro, Delaware

PW-2

Date

Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10

Flow Differential

(gal)

5,258,300 4,506,500 4,983,800 4,836,857 6,767,215 7,854,500 6,887,800 4,423,801 4,726,001 2,155,500 2,028,100 1,166,202

Time Differential

(days)

31 28 31 30 31 30 31 31 30 31 30 31

Time Differential

(min)

44,640 40,320 44,640 43,200 44,640 43,200 44,640 44,640 43,200 44,640 43,200 44,640

Up Time (AG/200)

(min)

26,292 22,533 24,919 24,184 33,836 39,273 34,439 22,119 23,630 10,778 10,141 5,831

Up Time

(days)

18.3 15.6 17.3 16.8 23.5 27.3 23.9 15.4 16.4 7.5 7.0 4.0

Up Time

%

59% 56% 56% 56% 76% 91% 77% 50% 55% 24% 23% 13%

Average Flow (gpm)

118 112 112 112 152 182 154 99

109 48 47 26

Notes: gal: gallons gpm: gallons per minute PW-2 has an approximate fiowrate of 200 gpm

Page 1 of 1

AR000460

Table 3 2010 Trichloroettiene Analytical Results Millsboro, Delaware

1/4/2010 1/11/2010 1/18/2010 1/25/2010 2/1/2010 2/9/2010 2/15/2010 2/22/2010 3/1/2010 3/8/2010 3/15/2010 3/22/2010 3/29/2010 4/7/2010 4/12/2010 4/19/2010 4/26/2010 5/3/2010 5/10/2010 5/17/2010 5/24/2010 6/1/2010 6/7/2010 6/14/2010 6/21/2010 6/28/2010 7/6/2010 7/13/2010 7/19/2010 7/26/2010 8/2/2010 8/9/2010 8/16/2010 8/23/2010 8/30/2010 9/7/2010 9/13/2010 9/21/2010 9/27/2010 10/4/2010

10/11/2010 10/18/2010 10/25/2010 11/1/2010 11/8/2010

11/15/2010 11/22/2010 11/29/2010 12/6/2010

12/20/2010 12/28/2010

PW-1 Influent Midpoint

130 140 220 190 160 120 150 230 130 190 220 260 240 260 250 210

280D 250D 220D 250D 240D 230D 210D

190D(190D) 150DJ 190D 250D 180D 180D 170D 160D 120D 180 370 180

160D

<0.50U, < 0.50U'' < 0.50U < 0.50U <0 50U < 0.50U < 0.50U < 0.50U <0 50U < 0.50U < 0.50U < 0.50U < 0.50U < 0 50U <0.50U < 0.50U < 0 50U

<0.50U(<0.50U) <0.50U < 0.50U < 0.50U <0.50U < 0.50U <0.50U 0.5UBJ

<0.50U(<0.50U) <0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U

i0.50U(<0.50U) < 0.50U < 0.50U

* System down for electrics * System down for electrics

150D 270 (260D)

170 150D 270D

< 0.50U < 0.50U < 0.50U

< 0 50U (< 0.50U) < 0.50U

* System carbon change 500D 450D 180D' 240D 400 410 820

< 0.50U < 0.50U < 0.50U < 0.50U

< 0 50U (< 0.50U) < 0.50U < 0.50U

Effluent < 0.50U < 0 50U <0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0 50U < 0.50U < 0.50U <0.50U < 0.50U

0.092J (<0.50U) < 0.50U <0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U

0.5UBJ (0.5UBJ) < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U < 0.50U

< 0.50U (< 0.50U) < 0.50U < 0 50U < 0.50U

repsirs repairs

< 0.50U < 0.50U

< 0.50 (< 0.50) < 0 50U 0.13J

i out

< 0.50U < 0.50U < 0.50U

< 0.50U (< 0.50U) < 0.50U < 0.50U < 0.50U

Influent 94 130 72 110 120 94 90 80 31. 94 73 52 68 77 66 66

70D 76D

I IOD(IIOD) 130D 160D 170D 200D 180D 190DJ 260D 1 (1) 1600 180D 240D 230D 210D 210 89

140(190) 280D 120 280 130D

1 32

64D 53D (55D)

48D 23D 16D 27D 13 84 3.4

0.42 (0.44)

PW-2 Midpoint < 0.50U < 0.50U < 0.50U < 0.50U < 0 50U < 0.50U <0.50U <0.50U < 0.50U <0.50U <0.50U < 0.50U <0.50U < 0 50U

0.25 < 0.50U 0.097J 0.16J

0.088J 063

0.46J (0.45J) 0.64 2.6

0.83 0.74UBJ

0.74 0.074J 0.052JL

0.085J (0.096J) 0 13 0 1

0.091J 0.4

0.65 0.43 0 2

0.37(0.46) , 0.17J

0.1 036 0.26

<0.50U 0.27J

< 0 50U < 0.50U (< 0.50U)

<0.50U <0.50U <0.50U <0.50U <0.50U <0.50U

Effluent < 0.50U < 0.50U < 0 50U <0.50U <0.50U <0.50U <0.50U <0.50U <0.50U <0.50U <0.50U <0.50U <0.50U <0.50U < 0.50U < 0.50U < 0.50U < 0 50U <0.50U

0.063J(<0.50/<0.50U) 0.055J < 0.50U < 0.50U 0.058J 05UBJ 0.059J

< 0.50U < 0.50U {< 0.50UJL)

< 0.50U < 0.50U < 0.50U < 0.50U < 0.50U <0.50U <0.50U

< 0.50U (< 0.50U) <0.50U <0.50U <0.50U < 0.50U < 0.50U < 0 50U < 0 50U

< 0.50U (< 0.50U)

< 0.50U < 0.50U <0.50U <0.50U <0.50U

<0.50U(<0.50U) < 0.50U

Change out performed. Vessel lead/lag configuration change Parenthesis denote s duplicate ssmple D: Diluted Ssmple U: FIsg indicates no detection for the compound J: Ssmple result flagged ss esfimated is below ttie mettiod detection limit B: Analyte was found in the associated method blank as well as the sample All results are in micrograms per liter (tjg/L) Sample results betwreen January 4, 2010 snd Apnl 19, 2010 provided by EA historical analyticsl tables

Page 1 of 1

AR000461

Table 4 Anion Analytical Results

Millsboro, Delaware

Sample ID

Sampling Date

WET CHEMISTRY

Bicarbonate Alkalinity as CaC03

Carbonate Alkalinity as CaC03

Chloride

Nitrate as N

Sulfate

PW-1 A

10/25/10

PW-2A

10/25/10

PW-1 A

12/28/10

PW-2A

12/28/10

Result (mg/L)

11.9

5.0

21.5

6.3

16.3

10.6

5.0

17.1

6.4

13.7

14.8

5.0

18.8

7.0

13.4

12.2

5.0

17.1

6.0

16.3.

Notes:

mg/L: milligrams per liter

Samples collected from influent sampling ports

AR000462

Table 5 Alternabve Discharge Screening Summary Millsboro, Delaware

Discharge Alternative

Reinjection - Use ot 1. Beneficial Reuse Piping

Network

Spray 2. Irngabon/Benefidal

Reuse

2 Surface water discharge to Millsboro Pond •

Overall Protection of Human Health and the Environment

This alternative provides a level of protection similar to that o( Ihe current system operation. Detailed hydraulic modebng suggests that re

injection can be accomplished without compromising the ability of PW-1 and PW-2 to maintain hydraulic control. This alternative will not affect protection of human health and the

environment.

If operated year-round, this alternative could provide a level ot piotection similar to that ot

the current system opeiation. PW-1 and PW-2 treatment systems will provide hydraulic

control which is sbll the primary objective. This alternative will not affect protection of human

health and the environment.

This alternative provides a level o( protection similar to that of the past system operation.

PW-1 and PW-2 treatment systems will provide hydraulic control which is still the primary objective. This alternative will not alfecl protection ot human health and the

environment. However, treatment for nitrates will likely be required before discharging to

surface water.

Effectiveness Evaluation

High: Reinjection allows for the aquifer to be recharged so there is no

loss in aquifer pumping potential.

High: Beneficial reuse will supply irrigation needs for the community. Treated groundwater will be sent directty into beneficial reuse Hne.

Moderate: Surface water discharge to Millsboro Pond will be an effective

discharge location however existing nitrate levels in Millsboro Pond Vrill

require further treatment of groundwater.

Implementability Evaluation

High: Existing beneficial reuse piping avoids installation of new conveyance

piping under existing roadways and makes this the fastest option to implement.

Injection wells and new piping from the beneficial reuse line mininruze

construction. II the current discharge line is not available to facilitate delivery of the treated groundwater to the injection well

locations the addition of new HDPE piping and valves between the treatment systems and the wells VMII be required. Construction

wilt likely require permits and road closures.

Moderate: Infrastructure will not be installed for another 2-3 years. Would need to be supplemented with another

discharge options when beneficial leuse demand is low.

Low: Lack of direct route to Millsboro Pond (or infrastructure piping v*\\ require the

need for construction through main streets. Existing high nitrate concentrations in

Millsboro Pond vrarrant the addition of ion exchange for nitrate treatment.

Estimated Schedule

Fastest Option to Implement: 3-6 Months

6-12Months It existing piping is unavailable for

use.

2-3 Years

1-2 Years

State/Community Concerns

The reintroducfion of treated groundwater back into the

Columbia Aquifer should not be a concern because TCE will have been removed. The treated Columbia formation vrater will be reinjected back

into the Columbia aquifer in a slightly different location in

essentially the same condition it was removed - except for the

treatment of TCE.

Discharge of treated groundwater via spray irrigation (or beneficial reuse should not be a concern. Delaware has a

long history of promoting beneficial reuse ol reclaimed

water.

Discharge of treated groundwater via surface

discharge should not be a concern as the effluent

discharged meets drinking water quality standards.

Relative Cost Evaluation

Moderate: Moderate capital for injection we\k but low 04M

costs to implement and maintain. 5450,000 capital

install. Estimated capital costs for construction of new

discharge piping are -approximately $150,000.

Low: Lowcapitalcosls; low O&M costs.

High: Moderate conveyance line capital costs S600.000; High ion exchange capital

costs $1,100,000; High annual O&M costs

5600,000.

Retained?

Yes: Fastest Option to Implement.

Yes. HoWBvei, significant limitations due to

implementation and inability (or year round end use.

Considered in conjunction with other technologies.

No' Intrastructure piping installation anid additional

design, equipment procurement, and installation will not allow for alternative to

be implemented in a reasonable timeframe.

Conclusion/ Recommendation

Yes, pursue Discharge Alternative 1

No, do nol pursue Discharge Allernalive 2

No, do not pursue Discharge Alternative 3

Notes: O&M - Operations & Maintenance USEPA - United States Environmental Protection Agency

AR000463

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LEGEND

- ^ Existing Manitotmg WeH

V Monitoring Well (ColumCiia Aqui(er)

'.< Monitoring Well (Bettiany Aquifer)

^ Uonrtonng Wall (Manokin Aquifer}

% Supply Well

SCALE IN F E E T

MILLSBORO, DELEWARE

EXISTING MONITORING WELL LOCATIONS

( ^ ARCADIS FIGURE

1

AR000464

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