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n Secondary Containment With Interstitial Monitoring

n Automatic Tank Gauging Systems

n Vapor Monitoring

n Groundwater Monitoring

n Statistical Inventory Reconciliation

n Other Methods Approved By DEP

n Tank Tightness Testing With Inventory Control (see pages 16-19)

This method combines periodic tank tightness testing with monthly inventory control. Tightness tests are tests performed by trained professionals. You must also use monthly inventory control. Inventory control involves taking daily measurements of tank contents and recording deliveries and amount pumped. Note: this combined method can be used during the first 10 years following new tank installation or upgrade of your existing UST. After that, you must use monthly monitoring methods. (This combined method can also be used temporarily, until December 1998, with tanks that have not been upgraded with spill, overfill, and corrosion protection.)

n Manual Tank Gauging (see pages 20-21)

Manual tank gauging can be used only for tanks of 2,000 gallons or less capacity. This method requires keeping the tank undisturbed for at least 36 hours each week, during which the contents of the tank are measured twice at the beginning and twice at the end of the test period. Each measurement is compared with the weekly standards on page 21. At the end of the month, you average the weekly tests and compare the results to the standards shown on page 21 to see if your tank may be leaking. This method can be used by itself only for tanks up to 1,000 gallons. Tanks between 1,001 and 2,000 gallons can use this method in combination with periodic tank tightness testing instead of inventory control. This combined method, however, can be used only during the first 10 years after tank installation or upgrade. (The combined method can also be used temporarily, until December 1998, with tanks that have not been upgraded with spill, overfill, and corrosion protection.)

n Secondary containment provides a barrier between the tank and the environment. The barrier holds the leak between the tank and the barrier so that the leak is detected. The barrier is shaped so that a leak will be directed towards the interstitial monitor.

n Barriers include:

n Clay and other earthen materials cannot be used as barriers.

n Monitors are used to check the area between the tank and the barrier for leaks and alert the operator if a leak is suspected.

n Some monitors indicate the physical presence of the leaked product, either liquid or gaseous. Other monitors check for a change in condition that indicates a hole in the tank, such as a loss of vacuum or a change in the level of a monitoring liquid between the walls of a double-walled tank.

n Monitors can be as simple as a dipstick used at the lowest point of the containment to see if liquid product has leaked and pooled there. Monitors can also be sophisticated automated systems that continuously check for leaks.

n The product level and temperature in a tank are measured continuously and automatically analyzed and recorded by a computer.

n In the "inventory mode," the ATGS replaces the use of the gauge stick to measure product level and perform inventory control. This mode records the activities of an in-service tank, including deliveries.

n In the "test mode," the tank is taken out of service and the product level and temperature are measured for at least one hour. Some systems, known as "continuous ATGS," do not require the tank to be taken out of service to perform a test. This is because these systems can gather and analyze data during many short periods when no product is being added to or taken from the tank.

n The ATGS must be able to detect a leak no larger than 0.2 gallons per hour with certain probabilities of detection and of false alarm. Some ATGS can also detect a leak of 0.1 gallons per hour with the required probabilities.

n ATGS have been used primarily on tanks containing gasoline or diesel, with a capacity of up to 15,000 gallons. If considering using an ATGS for larger tanks or products other than gasoline or diesel, discuss its applicability with the manufacturer's representative. Remember, do not use an ATGS if your UST is more than 1.5 times the capacity of the UST used in the third-party evaluation of that ATGS.

n Water around a tank may hide a leak by temporarily preventing the product from leaving the tank. To detect a leak in this situation, the ATGS should be capable of detecting water in the bottom of a tank.

n Vapor monitoring senses or measures "fumes" from leaked product in the soil around the tank to determine if the tank is leaking.

n Fully automated vapor monitoring systems have permanently installed equipment to continuously or periodically gather and analyze vapor samples and respond to a release with a visual or audible alarm.

n Manually operated vapor monitoring systems range from equipment that immediately analyzes a gathered vapor sample to devices that gather a sample that must be sent to a laboratory for analysis. Manual systems must be used at least once a month to monitor a site.

n All vapor monitoring devices should be periodically calibrated according to the manufacturer's instructions to ensure that they are properly responding.

n Before installation, a site assessment is necessary to determine the soil type, groundwater depth and flow direction, and the general geology of the site. This may only be performed by a New Jersey certified subsurface evaluator.

n Vapor monitoring requires the installation of monitoring wells within the tank backfill. The number of wells and their placement is very important. Only an experienced New Jersey certified contractor may properly design and construct an effective monitoring well system.

Groundwater Monitoring

n Groundwater monitoring involves the use of permanent monitoring wells placed close to the UST. The wells are checked at least monthly for the presence of product that has leaked from the UST and is floating on the groundwater surface.

n The two main components of a groundwater monitoring system are the monitoring well (typically a well of 2-4 inches in diameter) and the monitoring device.

n Detection devices may be permanently installed in the well for automatic, continuous measurements for leaked product.

n Detection devices are also available in manual form. Manual devices range from a bailer (used to collect a liquid sample for visual inspection) to a device that can be inserted into the well to electronically indicate the presence of leaked product. All devices must be operated at least once a month.

n Before installation, a site assessment is necessary to determine the soil type, groundwater depth and flow direction, and the general geology of the site. This assessment may only be performed by a New Jersey certified subsurface evaluator.

n The number of wells and their placement is very important. Only an experienced New Jersey certified contractor may properly design and construct an effective monitoring well system.

n SIR analyzes inventory, delivery, and dispensing data collected over a period of time to determine whether or not a tank system is leaking.

n Each operating day, the product level is measured using a gauge stick or other tank level monitor. You also keep complete records of all withdrawals from the UST and all deliveries to the UST. After data have been collected for the period of time required by the SIR vendor, you provide the data to the SIR vendor.

n The SIR vendor uses computer software to conduct a statistical analysis of the data to determine whether or not your UST may be leaking. The SIR vendor provides you with a test report of the analysis.

n To be allowable as monthly monitoring, a SIR method must be able to detect a leak at least as small as 0.2 gallons per hour and meet the state and federal regulatory requirements regarding probabilities of detection and of false alarm. Data must be submitted at least monthly.

n To be allowable as an equivalent to tank tightness testing, a SIR method must be able to detect a leak at least as small 0.1 gallons per hour and meet the state and federal regulatory requirements regarding probabilities of detection and of false alarm.

n The individual SIR method must have been evaluated with a third party test procedure to certify that it can detect leaks at the required level and with the appropriate probabilities of detection and of false alarm.

n Many tightness test methods are "volumetric" methods in which the change in product level in a tank over several hours is measured very precisely (in milliliters or thousandths of an inch).

n Other methods use acoustics or tracer chemicals to determine the presence of a hole in the tank. With such methods, all of the factors in the following bullets may not apply.

n For most methods, changes in product temperature also must be measured very precisely (thousandths of a degree) at the same time as level measurements, because temperature changes cause volume changes that interfere with finding a leak.

n For most methods, a net decrease in product volume (subtracting out volume changes caused by temperature) over the time of the test indicates a leak.

n The testing equipment is temporarily installed in the tank, usually through the fill pipe.

n For most methods, the test is performed by a testing company. You just observe the test.

n Manifolded tanks generally should be disconnected and tested separately.

n Depending on the method, up to 4 tanks can be tested at one time. Generally, an automated system is necessary to test 3 or 4 tanks at a time.

n Procedure and personnel, not equipment, are usually the most important factors in a successful tightness test. Therefore, well-trained and experienced testers are very important. In New Jersey, tank tightness testers must be certified by the DEP.

n UST inventories are determined daily by using a gauge stick and the data is recorded on a form. The level on the gauge stick is converted to a volume of product in the tank using a calibration chart, which is often furnished by the UST manufacturer.

n The amounts of product delivered to and withdrawn from the UST each day are also recorded. At least once each month, the gauge stick data and the sales and delivery data are reconciled and the month's overage or shortage is determined. If the overage or shortage is greater than or equal to 1.0 percent of the tank's flow-through volume plus 130 gallons of product, the UST may be leaking.

n Four measurements of the tank's contents must be taken weekly, two at the beginning and two at the end of at least a 36-hour period during which nothing is added to or removed from the tank. See the table on the next page.

n The average of the two consecutive ending measurements are subtracted from the average of the two beginning measurements to indicate the change in product volume.

n Every week, the calculated change in tank volume is compared to the standards shown in the table on the next page. If the calculated change exceeds the weekly standard, the UST may be leaking. Also, monthly averages of the four weekly test results must be compared to the monthly standard in the same way. See the table on the next page.

n Liquid level measurements must be taken with a gauge stick that is marked to measure the liquid to the nearest one-eighth of an inch.

n Manual tank gauging may be used as the sole method of leak detection for tanks with a capacity of 1,000 gallons or less for the life of the tank. Tanks between 551 and 1,000 gallons have two testing standards based on their diameter (see table). These tanks also may use a combination of manual tank gauging and periodic tank tightness testing for the life of the tank (see table for testing standards).

n No leak detection is required if the suction piping has (1) enough slope so that the product in the pipe can drain back into the tank when suction is released and (2) has only one check valve, which is as close as possible beneath the pump in the dispensing unit. If a suction line is to be considered exempt based on these design elements, there must be some way to check that the line was actually installed according to these plans.

n If a suction line does not meet all of the design criteria noted above, one of the following leak detection methods must be used:

n If a suspected leak is detected, a flow restrictor keeps the product flow through the line well below the usual flow rate. If a suspected leak is detected, a flow shutoff completely cuts off product flow in the line or shuts down the pump.

n A continuous alarm system constantly monitors line conditions and immediately triggers an audible or visual alarm if a leak is suspected. Automated internal, vapor, or interstitial line monitoring systems can also be set up to operate continuously and sound an alarm, flash a signal on the console, or even ring a telephone in a manager's office when a leak is suspected.

n Both automatic flow restrictors and shutoffs are permanently installed directly into the pipe or the pump housing.

n Vapor and interstitial monitoring systems can be combined with automatic shutoff systems so that whenever the monitor detects a suspected release the piping system is shut down. This would qualify as a continuous alarm system. Such a setup would meet the monthly monitoring requirement as well as the LLD requirement.

n Tracer methods do not measure pressure or flow rates of the product. Instead they use a tracer chemical to determine if there is a hole in the line. With tracer methods, all of the factors below may not apply.

n The line is taken out of service and pressurized, usually above the normal operating pressure. A drop in pressure over time, usually an hour or more, suggests a possible leak.

n Most line tightness tests are performed by a testing company. You just observe the test. The test must be performed by a New Jersey certified individual and company.

n For most line tightness tests, no permanent equipment is installed.

n In the event of trapped vapor pockets, it may not be possible to conduct a valid line tightness test. There is no way to tell definitely before the test begins if this will be a problem, but long complicated piping runs with many risers and dead ends are more likely to have vapor pockets.

n Some permanently installed electronic systems can meet the requirements of a line tightness test.