MEMORANDUM To: Case File #04-104 Through: James Shell, Chief Regulated Storage Tank Division From: Technical Branch Staff, Regulated Storage Tank Division Date: July 3, 2003 Subject: Corrective Action Plan Shell SuperStop #102 Rogers, AR ID #04000030 After a period of interim hazard abatement and remedial investigation, we have concluded a corrective action plan is necessary for the referenced site. This document describes how the case developed, where the Department’s regulatory interest lies, and what goals we propose for a solution. CASE DEVELOPMENT This case came to our attention on June 18, 2002, when employees of the Northwest (Goodyear) Tire Service located just south (across New Hope Road) of the SuperStop #102 reported that gasoline vapors were accumulating in the men’s restroom. The complaint was made to the facility. The facility notified the owner/operator (O/O), and the O/O reported the problem to ADEQ immediately. On that same date, an investigation conducted by the ADEQ-RST area inspector discovered a leaking O-ring on the submersible pump unit serving the unleaded regular-grade UST. The UST system was taken out of service. The O-ring was replaced; the UST system was tested and returned to service on June 19, 2002. Also on that date, a contractor/consultant retained by the O/O arrived on the site to begin a preliminary investigation and abatement measures. During this period (the exact time is unknown), the Northwest Tire Service arranged for a plumber to come in and replace the seal under the water closet in the men’s restroom. After this repair, vapor accumulation in the building diminished sharply. The O/O concluded the vapors were entering the buildings by advective vapor transport along utility conduits, and immediately set about installing a soil vapor extraction trench just down- gradient from the UST tankhold. The trench was completed by 6/21/02. However, the vacuum blower was not installed until 8/28/02. Continuous vapor recovery began on that date. Attachment #3 provides an accounting of the recovery to date. On 6/21/02, ADEQ requested a source investigation, preparatory to remediation. The investigation was reported out on 8/9/02. Although the O/O did not completely characterize the source (only on-site sampling was done), sufficient work was done to fill out a working site model, and much of the information has been used in this plan. On 10/4/02, after meeting with ADEQ-RST technical staff, the O/O proposed an additional investigation to meet the goals of ADEQ’s 6/21/02 request, and to continue the vapor extraction program. ADEQ has not yet responded to this proposal. CONCEPTUAL SITE MODEL The following profiles summarize what is currently known about the facility and the releases which are the concern of this document. A reasonably complete investigation has been conducted for this site, and more-detailed information can be found in the case file for the facility. . Facility Profile The SuperStop #102 is a C-store/retail gasoline operation on the NE corner of US 71 Business and New Hope Road (aka Arkansas Highway 94) in the southern part of Rogers, AR. A copy of the area map is included as Attachment #1. The current USTs serving the facility were installed in 1982 on a clean site, and updated by impressed current cathodic protection on 2/19/02. Three twelve thousand gallon tanks store three grades of unleaded gasoline. Pressurized FRP product lines serve four MPD islands in front of the store. Leak detection is Statistical Inventory Reconciliation. Attachment #2 provides a facility plan view. Release Profile The contaminants of concern are gasoline range organics. An inspection of the inventory records for the twelve-month period prior to the release indicated a cumulative shortage of about 1,910 gallons of unleaded regular gasoline. As of this writing, about 980 gallons equivalent product has been recovered by the abatement program. Insufficient information is available to estimate the remaining mass of contaminant. While inventory records for the facility are available and in fairly good shape, this facility has a history of releases, including one (LUST #04-003) in 1988 which was prosecuted by ADEQ as a clean-up. Anecdotal reports are available of sporadic vapor accumulations over the last few years in the Northwest Tire Service shop and also in a telephone vault south of the SuperStop along the east side of US 71B. Physical/Geological Profile The facility is located directly on cherty residual soils of the Boone Limestone. There are two geologic/hydrogeologic horizons beneath the site. The uppermost horizon is an epi-Karst zone, reaching from the ground surface (around 1360’ AMSL in the study area) down to an average of about 7 to 10’ bgs. The soils are residual clays with varying amounts of cherty gravel, in some parts of the site reworked by construction activities. About two feet of fill material similar to the native soil is present in the southern portion of the facility, for example. Standing groundwater is found in this horizon for a short time after rainfall events. Otherwise, a water-moist zone is present at near-saturation levels reaching from about 4 to 6’ bgs down to the top of the competent rock. Recharge of this unit is by direct infiltration, and discharge is by seepage into the competent Boone Limestone horizon below. Soil samples collected from this zone demonstrate elevated concentrations of COCs over much of the facility area, and the soils of this interval are believed to be the “source” which must be addressed. Significant horizontal contaminant movement within the epi-Karst horizon has been verified. While groundwater discharge from this horizon is ultimately downward, there is also a significant horizontal component to groundwater advection which is believed to be the transport mechanism for contaminants to reach the nearby utilities. It is also probable that preferential pathways have been created by construction rework and site utility installation, and these pathways are influencing the direction and speed of the horizontal movement. The Boone Limestone is the dominant surface formation in the area, comprising a relatively flat-lying plateau, with erosional features (streambeds and remnants of overlying formations) providing topographical relief. Groundwater in the Boone Limestone is recharged by direct infiltration and seepage from overlying residual soils. Discharge from this unit provides base flow to perennial streams such as (in this case) Prairie Creek, and springs, such as Diamond Spring, both to the northeast into the Beaver Lake Basin. EXPOSURE ASSESSMENT The facility is located in a well-developed commercial area in southern Rogers. The nearest residences are about ½ mile away, well outside the impact area. Attachment #1 is a map of the study area. Human Exposure Profile It is likely that some contamination from the site is making its way into the regional (Boone) aquifer. However, there is no beneficial use of this unit by human receptors near enough to be impacted by contaminants from this facility. The only known human exposure is to gasoline vapors accumulating in nearby buildings. The release came to our attention due to complaints of gasoline vapors in two businesses across Arkansas Hwy 94, to the south of the facility. Investigation conducted for the initial response action confirmed the vapors were entering the buildings through their sanitary sewer connections. A plumbing seal was replaced in the Northwest Tire Service facility, and we have received no further complaints. However, vapors continue to be present in the headspace of the sanitary sewer, and further impacts are possible with the deterioration of the plumbing systems for the affected buildings. Also possible is attainment of explosive vapor levels in the sewer itself. While direct public safety consequences from this condition are unlikely, an explosion could endanger utility workers, and at the very least, result in fairly extensive damage to the sewer itself. Since there is a strong correlation between rainfall events and the concentrations of vapors in the sewer, ADEQ has concluded the source of the vapors in the sanitary sewer is most likely to be contaminated groundwater and/or product infiltrating the sewer at some point. The City of Rogers has indicated the sewer line serving this area is in poor condition. Ecological Profile Although not verified by sampling, it is probable that some level of dissolved-phase contamination from the site is making its way into the regional aquifer. While there is substantial discharge to nearby waters of the state from the Boone unit (to springs and stream underflows), we do not believe regulated substances from the release are reaching known discharge points at this time. A discharge is possible in the future, however, if the source is not remediated. CORRECTIVE ACTION GOALS Conceptually, the goals for the corrective action are to – • Control human health exposures to harmful levels of regulated substance vapors in the study area. As a practical matter, any level of exposure above the odor threshold will be unacceptable. Since a critical element in the exposure pathway is the sanitary sewer, and since impacts to sanitary sewers are undesirable in and of themselves, attainment of this goal will be measured by monitoring the headspace of the sanitary sewer. • Prevent the spread of contaminants beyond the currently-impacted area and protect the resource value of the Boone groundwater unit by identification and remediation of source materials on the regulated facility and adjacent areas. Specific goals of the project are: • Attainment of the ATSDR odor threshold (0.025 ppm-v) for automotive gasoline (Gasoline Range Organics) in the headspace of the sanitary sewer line serving the immediate area. • Attainment of the non-aqueous phase liquid (NAPL) equilibrium concentration of Gasoline Range Organics (GRO) in the residual soils of the facility and surrounding area. This value is tentatively set at 500 mg/kg, although it may be modified by site-specific information developed during design of the remedial work plan. Alternately, an easier- measured surrogate indicator of attainment (such as soil vapor) may be adopted. • Attainment of the specific goals described above within 36 months of ADEQ approval of the Corrective Action Plan. • Verification of the attainments described above by not less than two years of post- remediation monitoring. CORRECTIVE ACTION PLAN TASKS In order of priority, the following actions must be taken to meet the goals of the CAP: • Offer the Draft CAP for public participation. • Design and implement a remedy for the source of the contamination, including provisions for monitoring/reporting progress toward the goals. A work plan for this task will be required, and the proposed remedy must be public noticed. • After the remedy has been fully implemented, conduct post-remediation monitoring to verify long-term attainment of the goals. • At the successful conclusion of the post-remediation monitoring period, decommission the corrective action program. • Issue a no further action letter to close out the project. PUBLIC PARTICIPATION Review/comment on this proposed Corrective Action Plan will be solicited in two ways: • A hard-copy of the Draft CAP will be sent under cover letter to the stakeholders directly impacted. These include the Owner/Operator, the Benton County Environmental Affairs office, the Rogers Water and Sewer Utility, and all landholders in the general vicinity of the release. A list of the proposed addressees is found in Attachment #4. • A notification of the availability of the Draft CAP for review and invitation to comment will be made by a legal notice advertisement in a newspaper of general circulation in the area. This action will be taken by the O/O, at the request of ADEQ, according to the procedure outlined in Attachment #5. The comment period will be thirty days, measured from the date upon which all stakeholders are notified. Comments should go to: Mr. Mike Shinn Regulated Storage Tank Division Arkansas Dept. of Environmental Quality P.O. Box 8913 Little Rock, AR 72219-8913 (501) 682-0989 firstname.lastname@example.org Comments may be received by ADEQ staff in any form, but only those attributable to specific persons and in writing will enter the casefile to be formally considered. At the end of the comment period, the comments will be evaluated by the technical staff of the RST Division, and if significant changes are advised, a new Draft CAP will be advertised. Otherwise, the CAP will be finalized, and work plans to implement the specified tasks will be requested in writing from the O/O. Attachment #1 Attachment #2 Attachment #3 Attachment #4 Following is a list of proposed stakeholders for public notice by direct mail-out. Mr. Tom McAlister Rogers Water and Sewer Utility P.O. Box 338 Roger, AR 72757 Mr. Mark Simpson Coulson Oil Company P.O. Box 68 North Little Rock, AR 72115 Mr. Al Inman Northwest Tire Service P.O. Box 293 Rogers, AR 72756 (479) 636-8018 Mr. Tom Peterson Ben Jack’s Arkansas Music 732 West New Hope Road Rogers, AR 72756 (479) 636-1125 Mr. Jim Ecker Benton County Environmental Affairs 215 East Central, Suite 8 Bentonville, AR 72712 (479) 271-1083 Mr. Clayton Eversole P.O. Box 183 Rogers, AR 72757 (479) 271-7758 Attachment #5 After a Corrective Action Plan has been drafted for a site, ADEQ will cause to be placed by the responsible party a legal notice in a newspaper of general circulation in the area adjacent to and directly affected by the release. In the absence of a local newspaper, the state-wide newspaper may be selected. The advertisement should only run one day. If it runs more than one day, the start of the comment period will be the last day the advertisement appeared. The legal notice must be substantially in the form below: ______________________________________________________________________ STATE OF ARKANSAS DEPARTMENT OF ENVIRONMENTAL QUALITY The Arkansas Department of Environmental Quality gives notice that a Corrective Action Plan has been drafted for the Shell SuperStop #102 facility, located at the intersection of US Hwy 71B and New Hope Road in Rogers, Arkansas. Pursuant to Title 40 Part 280.67(b), the Draft Corrective Action Plan is available for public inspection during normal business hours at: Arkansas Department of Environmental Quality Regulated Storage Tank Division 8001 National Drive Little Rock, AR 72209 Case File #04-104 Public comment on authorization, according to the procedures in the Draft Plan, will be received by the Department for not less than 30 days from the date of this advertisement. ADEQ may authorize implementation of the Corrective Action Plan before the public comment period is completed, if such action is necessary to protect public health and welfare.
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