Site Name: DAKHUE SAN LDFL
EPA ID: MND981191570 EPA Region: 05 Metro Statistical Area: 5120
260TH & HOGAN AVE, HAMPTON, MN 55031
Operable Unit: 02
ROD ID: EPA/ROD/R05-93/242 ROD Date: / /
Contaminant: GW
O&M Costs: Estimated Costs: $360,000
Keys: Benzene: Carcinogenic Compounds; Contingent Remedy; Direct Contact; Drinking Water Contaminants; Ground Water; Ground Water Monitoring; Institutional Controls; Lead; MCLs; Metals; PCE; Safe Drinking Water Act; Solvents; State Standards/Regulations; TCE; Toluene; VOCs
Abstract:
The 80-acre Dakhue Sanitary Landfill site is an inactive sanitary waste municipal landfill located in Hampton Township, Dakota County, Minnesota. Land use in the area is predominantly agricultural and residential. A gravel surficial aquifer, that is not a drinking water source, extends downgradient of the site. Most residents obtain their drinking water supply from nearby wells and/or a municipal water supply well located over 3 miles south of the site, both of which extract ground water from a deeper aquifer. The surficial and deep aquifers underlying the Dakhue site are thought to be hydraulically connected. From 1971, Dakhue Sanitary Landfill, Inc. owned and operated the landfill, and accepted mixed municipal and commercial waste and small amounts of industrial waste. Site operations ceased in 1988, but the landfill never received a final cover as part of the closure activities. State investigations conducted between 1983 and 1989 identified a variety of contaminants onsite in soil and ground water. EPA investigations identified elevated levels of VOCs, other organics, and inorganics in the surficial onsite aquifer, and it has been determined that the source of contamination is related to the improper disposal of municipal, industrial, and commercial waste in the landfill. The site has been divided into two OUs for remediation. A 1991 ROD addressed the source of the contamination and provided for capping of the landfill with a final cover, as OU1. This ROD provides a final remedy for the site and addresses onsite ground water contamination, as OU2. The primary contaminants of concern affecting the ground water are VOCs, including benzene, PCE, TCE, and toluene; and metals, including lead. SELECTED REMEDIAL ACTION: The selected remedial action for this site includes allowing ground water to naturally attenuate; providing for a contingent remedy to initiate a corrective action, if monitoring results indicate that ground water downgradient of the site exceeds the surface water standards set as "trigger levels" for certain contaminants; monitoring ground water; and implementing institutional controls, including ground water use restrictions. The estimated present worth cost for this remedial action is $360,000. PERFORMANCE STANDARDS OR GOALS: Chemical- specific ground water cleanup goals are based on SDWA MCLs, and include benzene 5 ug/l; bis(2-ethylhexyl)phthalate 6 ug/l; 1,2-DCA 5 ug/l; 1,2-DCE 70 ug/l; 1,2-dichloropropane 5 ug/l; methylene chloride 5 ug/l (proposed MCL); 1,1,2-TCA 5 ug/l; TCE 5 ug/l; and vinyl chloride 2 ug/l. Trigger levels for the ground water contingent remedy are based on surface water exceeding the following levels, and include aluminum 87 ug/l; chromium 11 ug/l; cyanide 5.2 ug/l; iron 221 ug/l; manganese 572 ug/l; silver 0.12 ug/l; and zinc 191 ug/l. INSTITUTIONAL CONTROLS: Ground water use restrictions will be implemented to prevent well development in the area.
Remedy:
This operable unit is the second for the site. The first operable unit involved capping the landfill to mitigate leachate formation. This operable unit includes the following major components:
* Institutional Controls contained in Dakota County Ordinance No. 114 and Minnesota Rules 4725.2000 and 4725.4300 which restrict well development; and
* Long term groundwater monitoring program to: (1) determine the migration of contamination; (2) assess trends in water quality in the Sand and Gravel aquifer; (3) verify that the deep aquifer is not affected; and (4) monitor contaminant levels in Judicial Ditch no. 1.