Coastal Derby - Smith / Benton Site
The Coastal Derby-Smith Benton Site is approximately two miles north of Benton, Kansas. The location is approximately one-half mile east of the intersection of 77th street and NW Butler Road, Butler County, Kansas.
On December 24, 1990, the Coastal Naphtha Pipeline ruptured releasing approximately 10,600 barrels (450,000 gallons) of product. Naphtha is a highly refined petroleum product consisting of benzene and other similar lightweight hydrocarbons that are used to blend various refinery products. The constituents of concern (COCs) at the site are benzene, toluene, ethylbenzene, and total xylenes (BTEX) along with Total Petroleum Hydrocarbons - Low Range Hydrocarbons (TPH-LRH). Following the rupture, Coastal Derby (Coastal) evacuated impacted residents; recovered naphtha from wells, trenches, and depressions; installed a downgradient slurry wall; completed soil borings; and installed groundwater piezometers to establish the extent of the contamination.
In 1991, Coastal entered into a consent order (CO) with KDHE to remediate the Benton Site. In 1992, Coastal entered into a CO with KDHE to remediate the related and nearby Smith Site. Since entering into the CO for the Smith Site, both Sites have been addressed together (Smith/Benton).
Initial investigation work in May 1991 included installing 29 soil borings and five collection trenches, as well as a groundwater extraction system to recover free product and impacted groundwater. By June 1992, 2,172 barrels of the free product had been recovered by the system. Air stripper pore aerators were installed in 1994 to treat extracted groundwater. An Evaluation Report submitted November 1994 provided the first details of site lithology, including a bedrock surface map that contoured the competent shale layer that prevents further vertical migration of contaminants. El Paso purchased Coastal in 1991 and took over Site activities. The groundwater extraction system suffered equipment failure and ceased operation in late 2009; the air stripper pore aerators had reached the end of their life span and were no longer repairable.
A 2005 pilot test work plan was revised in 2010 to focus efforts near the release location. On August 2, 2010, the System Evaluation, Additional Remedial Investigation, SVE/AS Pilot Test, and Dissolved Plume Stability Work Plan documents were approved. The SVE/AS Pilot Test was completed in July 2011, discovering more free products in the groundwater. A recommendation that groundwater extraction resume would require replacement of the groundwater extraction system. A geophysical pilot test was completed in spring 2012 to determine the extent of the free product.
A Draft Corrective Action Study (CAS) was submitted to KDHE in January 2013. This CAS included implementing interim remedial measures (IRM) for a multi-phase extraction (MPE) system. It was agreed to delay the completion of the CAS until the IRM was installed and data was available to assess its effectiveness. The IRM-MPE installed two new parallel recovery trenches and replaced the groundwater extraction system, combined with a soil vapor extraction system (SVE). The MPE system startup date was March 23, 2016, and the system continues to operate. The system was designed to remediate impacted soil and groundwater through enhanced biodegradation, dewatering, and volatilization of hydrocarbons. Site groundwater is currently analyzed for BTEX along with TPH-LRH.
In June 2018 a Final CAS was approved by KDHE that evaluated potential remedial alternatives. A Corrective Action Decision (CAD) has been drafted to outline the selected remedial alternative (Alternative 3) which includes: continued operation of the MPE system for five years followed by two years of semi-annual groundwater sampling for a plume rebound study and soil confirmation sampling, maintenance, and monitoring until the vapor phase mass removal no longer produces appreciable results, confirmation soil and groundwater sampling, and existing Environmental Use Controls (EUCs) to remain in place with additional EUCs to be obtained for two southern properties. The selected alternative also assumes contingency actions will be required after the five years of MPE operation, rebound testing, and confirmation soil sampling. Contingencies would include; MPE Restart, In-Trench Biosparge, Biostimulant Injections, and Long-Term Monitoring.
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