The rehabilitation of sites with petroleum contamination is an interesting and recurring problem that needs to be addressed as effectively as possible. As many different technological solutions can be utilized and each contamination site is somewhat unique in its problems and characteristics, a careful and detailed study of the available information is necessary to arrive at the optimal solution. Site remediation treatment technologies such as bioremediation, soil vapor extraction, thermally enhanced recovery, dual phase air sparged systems and other more exotic methods are constantly being developed to effectively meet varying contamination scenarios and treatment and cost efficiency requirements. The methodology and system that most effectively solves the existing contamination problem and is within budget need to be selected. Field supervision to ensure the correct erection and operation of the system is also of paramount importance to ensure that the cleanup goals will be met and the schedule maintained. In the paragraphs that follow, some of the approaches OHC would utilize to remediate petroleum contaminated sites are discussed, along with some case studies and methodology.

Typical gas stations are about one-half of an acre and are rectangular parcels of land that are about 200' by 250' located mostly at intersections. The parcel of land accommodates the office and or convenience food store, the pump islands, sometimes a car-wash and some repair shop and the underground storage tank pad. The tank pad usually has three 10,000-gallon underground storage tanks and is about 40' by 30'. Leaks usually occur at the dispensers, interconnecting piping, tank fill pits and the actual tank walls. Using the tank pad area and the dispensers in the pump islands as a focal point, a leaking underground storage tank system would thus have a circular areal zone of contamination with a diameter of 100'. Assuming a vadose zone of 10' and a saturated zone of 10' and a porosity of 20%, the vadose air volume that would have to vacuum extracted and treated would be about 15,700 cubic feet and the saturated zone water volume to be extracted and treated would be about 117,400 gallons. Thus a system that has vapor phase capacity of 100 cfm and a liquid phase capacity of 2 gpm will have the capability of extracting the vapor in about 8 hours and the groundwater in about a month. Thus operating the system for a few months will give several times of cleanup cycles of the vadose and saturated zone contaminants - a concept that has been accepted by many regulatory agencies and used in the treatment of numerous contaminated sites.

OHC has researched the dynamics of vadose and saturated zone contamination and the various remediation approaches than can be used to effect cleanup. We realized early on that using conventional pump and treat systems with activated carbon drums, air stripping towers and the like simply lead to long treatment times, an unwieldy assortment of equipment that is hard to maintain and enormous expenditure in time and money to the client. After considerable modeling of groundwater and vadose zone, vapor extraction with average transmissivity, porosity and other parameters that prevail over most of Florida, we realized that sparging the saturated zone and driving the contaminants into the upper vadose zone and then extracting them via a powerful soil vapor extraction unit was the key to effectively and economically achieve cleanup objectives. Incorporating a catalytic thermal destruction unit, with a fair amount of overcapacity, completed the total operational flexibility of the system. Adding the possibility of using nitrogen and or hot exhaust from the catalytic unit ensured even more effectiveness as it then could address iron fouling which is endemic in Floridian groundwater due to the high iron and mineral content. For typical gas station sites, three of these wells, with a cone of influence of about 30 feet will optimally cleanup the contaminated area in less time, with less expenditures, and without the need to purchase or lease long term equipment that is large, expensive, obtrusive and very difficult to maintain.

OHC is very cognizant of the amendments to the storage tank rules by the FDEP over the past few years. These rule changes have mandated staggered deadlines for both the underground and aboveground petroleum storage tanks in terms of upgrades of the tanks themselves and also interconnecting piping and other appurtenances. For instance, FAC 62-761.510 stipulates that by the end of 1998 all existing underground storage tank facilities should have secondary containment, automatic line leak detection, overfill protection and liners for the dispensers. OHC staff have worked on a number of tank removal and upgrade projects to ensure storage tank system compliance with the regulations.

Tank removals are, in most cases, surprises in terms of the size of the tank thought to be present underground. This arises mainly from the fact that most of the tanks removals are discovered during site clearance and renovation work and no records or regulatory information exists regarding these tanks - they are very old unregistered tanks about which no information is available. Another factor is that, when records are sketchy, the size of the tanks are often underestimated and a suspected 500 gallon used oil tank turns out to be a 1,000 or 2,000 gallon tank. Not only does this change the excavation and removal scope in terms of time and cost, but often the residual oily liquid than needs to be pumped changes quite considerably in volume, adding to the cost. OHC has worked on numerous such projects with reputable tank removal contractors and has a good working relationship to minimize these type of unforeseen contingency costs and times. Again, in some cases, field considerations may dictate that the tank be not removed but closed in place. OHC often recommends such alternatives if it is in the best interest of the client, which, in this case, will be the Manatee County Government.

Tank closure requirements have been revised as of June 1997 by the FDEP. The Storage Tank Regulation Section in the Bureau of Waste Management has provided guidelines to meet the FAC 62-761 requirements. These guidelines provide detailed requirements for the sampling of soil and groundwater, the various EPA test methodologies, sampling intervals and closure report requirements. OHC's Project Manager, Engineer and Geologist have completed numerous tank closures and are conversant will all the detailed requirements to ensure that tank closures are complete and accepted by the FDEP and any relevant locally contracted county program. An instance of these new guideline requirement is sampling of associated piping and dispensers. Soil samples are required every 20 feet of product transfer line, two feet below the line level or immediately above the groundwater table if it is shallower. As groundwater samples at these locations will be at the discretion of the FDEP or local program, OHC's Project Engineer will coordinate this with the appropriate liaison person to ensure that the guidelines are followed. OHC's Project Manager will often contact the liaison person ahead of the tank closure work schedule to allow for these type of requirements. OHC's Project Engineer will make sure that tank closure assessment form and report is submitted to the FDEP District Office as soon as the tank closure work is completed, well ahead of the sixty day window allowed by the FDEP and will follow up and expedite any additional work necessary with the FDEP so that the client will receive a satisfactory closure letter from the FDEP.

OHC firmly believes that contamination assessment is the backbone of the entire site remediation phase of cleanup. At the expense of sounding like a cliché, all the most expensive and efficient remediation technology will not serve any purpose if it is deployed in the wrong place and in the wrong way due to an inaccurate and or inadequate assessment. OHC's Project Geologist has much experience with respect to petroleum and hazardous waste contamination assessment. He will ensure that the FDEP and local program requirements for contamination assessment are followed so as to obtain CAR approvals which are vital in the sequence of steps in the cleanup of contaminated sites. Adequate contact and liaison with the FDEP and local program staff will be maintained to allow the review and approval of assessment plans. OHC realizes the importance of obtaining the comments and incorporating the requirements of FDEP and local program engineers and specialists. Communication with these personnel early in the project often provides for a timely review and approval of contamination assessment plans.

OHC is aware of the important role contamination assessment plays in the rehabilitation of petroleum contaminated sites. Contamination assessment defines and delineates the various contaminant chemicals and provides the basis of the remedial action methodology that follows. Items such as site history, geology an hydrology need to be accomplished in meticulous manner to allow a good engineering remedial plan that will cost effectively and efficaciously solve the contamination problem. The number and placement of deep an shallow wells will determine the horizontal and vertical extent of contamination. OHC's Project Geologist is very experienced in the design and specification of monitor wells and the management of the drilling and installation. OHC will judiciously request soil and groundwater test parameters to ensure that the resultant CAR will satisfy the FDEP and local program requirements. Close and effective liaison with the local program staff often ensures prompt approvals of contamination assessment plans and reports which will help in speedy remediation of contaminated sites.

OHC will complete contamination assessments for the Manatee County Government following the new ASTM E 1903-97 guidelines for Phase II Environmental Site Assessments. These newly released guidelines provide procedures for the selection and use of drilling and soil sampling techniques, classifying and describing soils, design of monitor wells and sampling and monitoring groundwater using direct-push equipment. OHC realizes that not only does the use of prescribed methods provide a proper evaluation of the presence or absence of environmental contamination but also contributes to quick regulatory review and approvals.

The release and spill of hazardous chemicals, such as mercury, sulfuric acid and chlorine, pose a health risk to any workers in the immediate vicinity and possibly to the public in the general vicinity depending upon the amount and severity involved. OHC staff have responded to mercury and petroleum release situations and have effectively contained and dealt with such incidences.

OHC's Project Manager and Engineer will ensure that the proper steps are taken in these instances to protect the public and any workers involved from immediate danger and then manage the effective cleanup of spill or release. OHC staff are well versed in the various containment methods used in petroleum, acid and other hazardous material release situations. A project specific safety plan will be established and followed to ensure that the cleanup crew are adequately protected from the hazardous materials than are been dealt with. OHC will pay particular attention to the effectiveness of the decontamination area and the proper temporary storage of hazardous materials prior to removal and disposal. OHC will also ensure that all necessary pre-burn tests and chain of custody, manifests etc. are meticulously completed to allow report acceptance and closure with the FDEP and any other local program. All OSHA requirements will be adhered to when completing hazardous material removal work.

OHC is an equal opportunity employer.