FIVE-YEAR REVIEW REPORT

Army Creek Landfill

Superfund Site

New Castle, Delaware

Prepared by:

U.S. Environmental Protection Agency

Region III

Philadelphia, Pennsylvania U.S. Environmental Protection Agency Region III Hazardous Site Cleanup Division Five-Year Review (Level I) Army Creek Landfill (EPA ID# DED980494496) New Castle, Delaware

I. Introduction

Purpose

This review is conducted pursuant to section 121(c) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as amended (CERCLA), 42 U.S.C. § 9621(c); section 300.400(f)(4)(ii) of the National Oil and Hazardous Substances Pollution Contingency Plan, 40 C.F.R. Part 300 (as amended); and OSWER Directives 9355.7-02 (May 23, 1991), 9355.7-02A (July 26, 1994), and 9355.7-03A (December 21, 1995). It is a statutory review. The purpose of a five-year review is to ensure that a remedial action remains protective of public health and the environment and is functioning as designed. This document will become a part of the Site file. This Level I review is appropriate for the Army Creek Site because both the hazard source and containment technology are well understood by EPA.

Site History and Characteristics

The Army Creek Landfill located in New Castle County, Delaware is a 60-acre abandoned sand and gravel quarry that was operated by New Castle County (County), from 1960 through 1968, for disposal of 1.9 million cubic yards of municipal and industrial waste. The site is bordered to the south and east by Army Creek, which discharges into the Delaware River one mile to the east. Another National Priorities List (NPL) site, the Delaware Sand and Gravel Landfill, is located immediately across Army Creek to the east of the site.

In 1972, ground water contamination was discovered in a residential well located in the adjacent Langollen Estates housing development. The Artesian Water Company (Artesian) maintains a public drinking water supply well field one-half mile downgradient of the site. Contaminants had not yet reached the Artesian wells.

To minimize the immediate threat, New Castle County installed a series of ground water recovery wells between the landfills and the public supply wells. In addition, Artesian’s State- permitted withdrawal rate was reduced and capped and Artesian’s water supply lines were extended to all residents in Langollen Estates.

2 The Army Creek Landfill site was promulgated to the NPL in September 1983. Subsequent investigation of the underlying Upper Potomac aquifer identified a plume of organic (e.g., benzene, methylene chloride, and bis 2-chloroethyl ether) and inorganic chemicals (e.g., cadmium, chromium, mercury and nickel) migrating from the landfill. The intermingled contaminant plume from the two contiguous landfills is intercepted by the ground water recovery wells operated by the County.

EPA managed the cleanup decision-making process through the development and publication of two Records of Decision (RODs). The first operable unit ROD (ROD-1), issued in September 1986, selected a remedy for source controls. The second operable unit ROD (ROD-2), issued in June 1990, selected an appropriate treatment level for recovered ground water prior to its discharge to the adjacent surface water body, Army Creek. ROD-1 identified a two-phased approach:

Phase I (1) Install a RCRA-type cap over the landfill (2) Continue operation of the recovery well network (3) Evaluate the effectiveness of the system over a five year period

Phase II (1) Based on monitoring data collected during the first five years after capping the landfill and treating the recovered water, a determination will be made on whether upgradient ground water controls are necessary (2) Continue evaluation of the effectiveness of the system (3) Operation and maintenance

ROD-2 selected a remedial action that includes the construction and operation of a water treatment plant capable of reducing the concentration of iron (# 1 mg/kg) in recovered ground water. In addition, the remedy requires long-term monitoring of extracted ground water, surface water, sediments and associated wetlands.

The United States, the State of Delaware and 18 cooperating PRPs entered into a Consent Decree on September 12, 1991 (United States v. BP America et al. Civil Action No. 91-409). In accordance with the consent decree, the PRPs agreed to implement the remedy selected in both Records of Decision.

The ground water extraction system captures the intermingled contaminant plume migrating from both the Army Creek and adjacent Delaware Sand and Gravel NPL sites. The single water treatment facility currently treats an estimated 500,000 gallons of contaminated ground water per day prior to its discharge to Army Creek. As of September 1, 1998, approximately 955 million gallons of contaminated water were treated.

Long-term environmental monitoring has been performed in accordance with the EPA-

3 approved Operation and Maintenance Plans (O&M). Monitoring and maintenance have been performed with reports submitted to EPA on a monthly basis.

II. Discussion of Remedial Objectives; Areas of Compliance/Noncompliance

The remedial objectives are 1) to prevent direct contact with buried wastes; 2) to reduce infiltration of rainwater and resulting contaminated leachate to ground water; 3) to intercept contaminated ground water as it moves from the landfills; and , 4) to treat recovered ground water so that it can be safely discharged to Army Creek. Ground water and surface water monitoring has been conducted to confirm that the objectives have been achieved.

In accordance with the Consent Decree, the remediation tasks were split among the PRP group and carried out by two separate contractors under the designation of Work-1 (landfill cap) and Work-2 (ground water collection and treatment). The following is a summary of the remedial actions conducted to meet the remedial objectives.

Work-1

The Work-1 activities included construction of a multi-layer landfill cap. The following is a brief description of each of the cap system elements from the bottom up:

•site foundation fill served as a leveling course between the original grade and the geomembrane base layer and established the base for the required cap slope of 2.5 to 3.0%. •12-inch thick geomembrane base layer served as a secondary source of containment for the surface water migrating through the cover soils. •geomembrane is a 40 mil LLDPE (Linear Low Density Polyethylene) material, continuously bonded, to form an impermeable barrier to prevent water from passing through the underlying wastes buried in the landfill. •geonet is a continuous polyethylene web that serves as the cap drainage layer. •geotextile is a non-woven needle-punched fabric placed between the cap cover layer (select fill) and the cap drainage layer (geonet). •18-inch thick select fill material layer is the primary cap cover over the installed geosynthetics. •6-inch thick topsoil layer is the top cap cover over the installed geosynthetics. •The seeding mix for erosion control consisted of annual and perennial grasses plus wildflowers.

Additional major design elements included:

•Eighty-two (82) permanent gas vents were augered into the existing landfill material •security fence around the perimeter of the landfill •Eight (8) permanent settlement monuments were installed to monitor settlement

4 The landfill cap construction activities were implemented from May 1992 through November 1993.

Work-2

The Work-2 activities included construction of a water treatment plant and required piping to route recovered ground water to the water treatment facility.

The ground water recovery system consists of nine extraction wells, all required piping, an equalization tank, and a lift station necessary to convey the recovered fluids to the treatment building. The treatment plant consists of a cone aerator, precipitation (pH adjustment and polymer addition), an upflow sand filtration system, a lamella thickener, a filter press and all associated transfer pumps and controls. The complete ground water recovery and treatment system (excepting the recovery wells, which were already in place) was installed during the period of June 1992 through December 1993.

Environmental Monitoring

The long-term monitoring and maintenance plans were initiated after construction was completed. The Work-1 O&M plan focuses on maintaining the landfill cap system. The Work-2 O&M plan includes sampling the treatment plant effluent to confirm compliance with limits, monitoring the ground water divide maintained by the recovery wells, and sampling and testing ground water quality downgradient of the landfills to measure any trends in water quality as a result of source control measures employed. See attachment for a summary of routine monitoring activities associated with Work-2.

Work-1 - A facility inspection is performed and a report submitted on a quarterly basis. Each quarterly inspection has confirmed that the integrity of the cap has been maintained, erosion control measures are effective, air quality at the perimeter of the landfill is safe and perimeter fencing is in place.

Work-2 - Water level measurements across the monitoring point system collected on a weekly basis confirm that the ground water divide has been maintained between the landfills and the Artesian’s public supply wellfield.

The discharge monitoring reports submitted monthly document that the water treatment plant continues to meet the numeric performance standards established in ROD-2. Iron concentration in plant effluent is maintained well below the 1.0 mg/L criterion. Acute and chronic bioassay tests are performed on treatment plant effluent quarterly. Treatment plant effluent has consistantly passed the acute toxicity tests; however, both effluent and control water collected from an unaffected public drinking water well has routinely failed the chronic toxicity tests.

5 The chronic toxicity test protocol employed involves counting the number of offspring produced by a group of ceriodaphnia dubia (water flea) exposed to water collected from the target source. The evaluation is concurrently performed on 1) clean ground water collected from a nearby well known to be unaffected by the landfill, and 2) clean control water purchased from a laboratory supply vendor. The number of offspring produced by water fleas living in extracted ground water is statistically smaller than the number produced by water fleas living in control water from the laboratory supply vendor, without respect to Site-related contaminants. Federal and State regulators and bioassay experts are aware of this phenomenon and are currently evaluating the possibility of modifying the qualitative testing required of the treatment plant effluent. The inherent difficulty of aquatic organisms to produce a statistically equal number of offspring in freshly extracted ground water is not considered to be a failure of the plant to meet performance standards.

The ground water recovery and treatment system has been constructed in accordance with the RD plans and specifications and is working toward eventual aquifer remediation.

Site Visit Performed to Assess the Effectiveness of the Remedy

On September 25, 1998, Eric Newman, EPA RPM conducted a site inspection. Upon arrival at the water treatment plant, Mr. Newman met with Mr. Chris Candella of Clean Tech, New Castle County’s environmental consultant overseeing operation, maintenance and monitoring at the Army Creek site. Mr. Newman had reviewed all monthly, quarterly and annual reports documenting O&M activities prior to the Site visit. During the facility inspection, in interview format, Mr. Candella confirmed that remedial objectives are being met. The water treatment plant has been meeting effluent performance goals and Mr. Newman observed that the receiving stream is no longer orange in appearance.1 Sludge generated by the plant is routinely tested and is not a RCRA-characteristic waste. The water treatment plant is tended by a full-time operator employed by Clean Tech. Clean Tech has subcontracted the day-to-day operations associated with monitoring the ground water recovery well system to Tetra Tech, Inc., with oversight provided by Clean Tech. Tetra Tech has been tasked with optimizing the system while maintaining the ground water divide between the landfills and the public supply wells. The goal is to maintain the divide while minimizing the ground water pumping rate to maximize cost- effectiveness and reduce impact to Artesian’s well field. From the water treatment plant office Mr. Newman conducted a telephone interview with Mr. Chris Geiger, Tetra Tech. Mr. Geiger confirmed that each of the nine recovery wells in the system are operable, however, Tetra Tech has been able to maintain the divide by pumping three of the wells continuously and using the other six wells intermittently. Mr. Geiger stated that the monthly potentiometric maps document the efficacy of the approach. Mr. Newman confirmed the statement with a detailed review of

1 Prior to treatment plant operation, surface water in Army Creek was orange due to high iron concentrations, orange precipitate could be observed coating the creek bottom.

6 historical maps.

Mr. Newman and Mr. Candella drove to the landfill to inspect the property and evaluate the integrity of the landfill cap. The perimeter of the landfill was secured by chain-link fence with a locked gate. The storm water and erosion control system was operable. No surface erosion was evident and the perimeter drainage ditch was unobstructed. No significant differential settlement has taken place2. Visual inspection confirmed site grading is relatively unchanged and all gas vents were intact. Mr. Candella informed Mr. Newman that the trapping and relocation of ground hogs had successfully prevented any damage to the integrity of the cap. Mr. Candella confirmed that water level measurements collected at gas vent locations document that the ground water mounding within the wastes has decreased. On average, the ground water elevation is slightly lower than pre-cap data meaning that less buried waste is saturated.

On October 21, 1998, Mr. Newman conducted a telephone interview with Mr. Thomas Neiger, President of Langollen Estates Civic Association. Langollen Estates is a residential housing development south of the Site. Mr. Neiger commended EPA, expressed satisfaction in the condition of the Site and stated that no community members have indicated any complaint with the former landfill.

III. Recommendations

The remedy is in conformance with the ROD and no further action is recommended at this time.

Through performance of this review, EPA did receive a commitment from PRPs at the adjacent Delaware Sand & Gravel site to share all analytical results and water level measurements collected from the 10 monitoring wells located on that site with Army Creek representatives. The shared data will augment the existing ground water monitoring point system and enhance the tracking of the ground water divide.

EPA will work with the State to develop a more appropriate method to measure chronic toxicity of treatment plant effluent. It is agreed by all parties that clean ground water collected from background locations fails the standard chronic toxicity test which was developed for surface water sources. Therefore, EPA does not believe this to be a remedy performance difficiency.

In addition to this statutory five-year review, the Army Creek selected remedy requires

2 Eight settlement monuments are surveyed annually. Elevations recorded November 1997 compared to as-built drawings document relatively uniform settlement ranging between -0.16 and -0.89 feet.

7 that the effectiveness of the remedy be evaluated for a five-year period from the point that the source control component of the remedy is in place. The intent of the remedy mandated evaluation will be to determine if upgradient ground water controls are necessary. A significant sampling effort focusing on the water and sediment quality in the adjacent stream will be completed in 1999. This 5-year Evaluation Report is anticipated Spring 2000.

IV. Statement on Protectiveness

I certify that the remedy selected for this Site remains protective of human health and the environment.

V. Next Five-Year Review

The next five-year review will be completed no later than June 2002.

8 ATTACHMENT – ARMY CREEK FIVE-YEAR REVIEW

ARMY CREEK TREATMENT PLANT MONITORING ACTIVITIES MONTHLY REPORT FOR SEPTEMBER 1998

DATE PROJECTED PASSED PERFORMED DATE LAST SUBMISSION OR ACTIVITY THIS MONTH PERFORMED OF RESULTS FAILED WELL LEVELS Water Levels Checked - Weekly 9/4, 9/11, 9/17, 9/24 8/7, 8/13, 8/21, 8/28 10/10/98 N/A Water Levels Checked - Monthly 9/24 8/28 10/10/98 N/A TREATMENT PLANT EFFLUENT Priority Pollutants (Quarterly) ------11/10/98 N/A Bioassay (Quarterly) 9/20 – 9/25 --- 11/10/98 N/A Flow - Daily 9/1 – 9/30 8/1 – 8/31 10/10/98 N/A Flow - Monthly Average 9/30 8/31 10/10/98 Passed TSS (Weekly) 9/1, 9/8, 9/14, 9/21, 9/28 8/3, 8/10, 8/17, 8/24 10/10/98 Passed Iron (Weekly) 9/1, 9/8, 9/14, 9/21, 9/28 8/3, 8/10, 8/17, 8/24 10/10/98 Passed pH (Weekly) 9/1, 9/8, 9/14, 9/21, 9/28 8/3, 8/10, 8/17, 8/24 10/10/98 Passed RECOVERY WELLS Priority Pollutant VOCs (Annually) --- 6/15 – 6/16/98 11/10/98 N/A Influent Iron Composite (NCC) --- 6/1, 6/8, 6/15, 6/22, 6/29 Monthly* N/A pH (Monthly by NCC) --- 6/1, 6/8, 6/15, 6/22, 6/29 Monthly* N/A BOUNDARY WELLS Priority Pollutant VOCs (Quarterly) --- 6/15 – 6/16/98 11/10/98 N/A Inorganics (Quarterly) --- 3/26/98 --- N/A Organics (Quarterly) --- 3/26/98 --- N/A ARMY CREEK HABITAT Habitat Report (Semi - Annually) 7/31/98 10/31/98 11/10/98 N/A NOTES: N/A = Not Applicable --- = Not Conducted This Month * = Available at NCC

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TABLE 1

RECOVERY WELL FIELD PUMPING RATES ARMY CREEK

September 1998

Monthly Most Recent Wells 9/4/98 9/11/98 9/17/98 9/24/98 Average Well Rehabilitation (mgd) (mgd) (mgd) (mgd) (mgd) Completion Date RW-1 .213 .199 .193 .220 .206 2/17/98 RW-10 .248 .225 .246 OFF .240 2/9/98 RW-11 OFF OFF OFF .219 .219 10/2/96 RW-12 OFF OFF OFF OFF .000 10/1/96 RW-13 .179 .153 .161 .176 .167 2/25/98 MW-27 OFF OFF OFF OFF .000 8/6/97 MW-28 OFF OFF OFF OFF .000 6/23/97 MW-29 OFF OFF OFF OFF .000 2/4/98 MW-31 OFF OFF OFF OFF .000 6/30/97 Recovery Well Field Total Discharge Rates * 0.605 0.605 0.619 0.576 Artesian Water Company Wells AWC-2 MNW MNW MNW MNW AWC-6 OFF OFF OFF OFF AWC-7 MNW .518 .533 .533 AWC-G3 .806 .864 .864 .835 AWC-K1 .490 .475 .504 .461

(mgd) - million gallons per day * - Based on treatment plant influent flow rates MNW - Water level meter not working TABLE 2

GROUND-WATER LEVEL ELEVATIONS - WEEKLY ARMY CREEK

September 1998

Top of Casing Well ID # Elevation 9/4/98 9/11/98 9/17/98 9/24/98 (a) (a) (a) (a) (a) AWC-2 65.55 IN IN IN IN AWC-6 57.03 WO WO WO WO AWC-7 48.09 -39.83 -41.79 -41.69 -43.01 AWC-G3 20.57 WO WO WO WO AWC-K1 27.25 -58.67 -59.16 -59.86 -60.07 MW-1A 7.94 -22.24 -22.68 -22.68 -20.56 MW-27 12.10 -19.86 -20.71 -20.72 -19.76 MW-28 21.89 -19.19 -19.42 -19.51 -19.73 MW-29 17.91 -16.71 -17.05 -17.06 -17.32 MW-31 14.70 -14.28 -15.18 -14.42 -22.52 MW-41 12.48 -25.57 -25.75 -25.85 -24.08 MW-69 18.91 -17.64 -17.76 -18.04 -18.09 RW-1 9.64 -68.16 -68.04 -66.73 -66.46 RW-10 9.68 -47.35 -47.13 -46.34 -19.71 RW-11 9.08 -22.33 -22.86 -22.92 -58.02 RW-12 13.40 -16.40 -16.59 -16.61 -16.82 RW-13 7.87 -34.99 -36.94 -36.67 -35.94

(a) - Feet mean sea level IN - Port inaccessible WO - Well obstructed TABLE 3

GROUND-WATER LEVEL ELEVATIONS - MONTHLY ARMY CREEK

September 1998

Top of Casing Ground-Water Well ID # Elevation Elevations (a) (a) LAYNE 19.25 Destroyed TW-3 17.66 Destroyed TW-4 18.15 -12.01 DGC-1S 40.21 Well Abandoned DGC-2S 32.31 Inaccessible DGC-7S 30.22 -14.54 DGC-9S 41.51 Well Abandoned MW-18 7.37 -21.74 MW-20 45.41 -23.59 MW-34 7.70 -21.68 MW-38N 35.99 -22.98 MW-40 35.95 -23.50 MW-45 24.31 -16.88 MW-49N 55.31 -27.66 MW-54 26.33 -5.67 MW-56 23.09 -11.87 MW-57 15.20 -11.80 MW-58 11.70 -8.25 MW-66 9.24 -28.57 MW-67 9.13 -21.28 MW-68 9.46 -19.96 22N 54.86 -24.85 26N 36.87 -28.71 BW-1 26.54 -23.68 BW-2 19.27 -24.16 BW-3 7.80 -21.85 C-1 35.18 15.96 C-2 30.00 Dry C-3 27.02 Dry B-18 26.31 26.31

(a) - feet mean sea level