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.