COMPLIANCE INFO_1985-2006 - Laserfiche WebLink

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OWWO 10i If i . r A '.w.! � • 'd1 0 depth, tit.) ry, .•r r .�t:.-es:-'eve.ai �..:ueC�r�w+y.r:i•.ir'vw � �. r�r wre� _ ?..ye.'� •-.�..t•a.. a :a i �` ` 6--• .. •t 141 i Native r %oils! i :r a•: r :} .' :;.:P ,11,• +' �'•''.`swr �.. v � .. >ti .. `••fit • -f too e 74E Z •. •• a a, t'ttt :c- ver '. a t �� .� - w, ®, 't e'er, Int- a r.•, ,T. ' - '.Va. RtiCr Otgfl:L�t. path r volt Z. V. r P"1 r GOt01eM storage tOAk a,• `:10 15 1 e. �� - . � - '.. .. •eve. ,`- ••.a. �• � �i differential between the release at or below the surface and detection at the groundwater surface ip an acceptable time period. Unfortunately in this case, groundwater monitoring as a leak de- tectio.n system would result in contam- ination of an acceptably large zone of Boit below the tank before contamina- tion would be detected in the ground- water monitoring well. A system of leak detection was nec- essary which could detect variations in the soil immediately adjacent to the tanks. Two existing technologies were considered. the tensiometer/lysimeter system and soil vapor monitoring. The tensiometer/lysimeter system detects changes in the moisture content of the soils and therefore can detect moisture content variations due to leakage from underground tanks. However, since the tanks store gasoline, which con- tains highly volatile, combustible components• soil vapor monitoring as a means of leak detection was deter- mined to be the most appropriate tech- nology. System And Component Description The subsurface monitoring system selected and installed at the site was intended to detect the presence of com- bustible vapors in the soils adjacent to and below the tank. Since gasoline va- pors are laterally dispersive, they can be readily detected in soil gas wells. The system components included two subsurface soil gas wells. traffic bear- ing access boxes for each well, a com- bustible vapor sensor in each well, arts a master control and alarm panel. The soil vapor wells were two-inct diameter PVC vapor wells. perforatec S to 15 feet below the surface installec as shown in the Well Location Plan. Figure 1. A graded sand pack w& - placed around the perforated section of each well. The well was backfills with native soils around the solid sec tion to a depth of 4 feet below tht ground surface (top of the storag, tank). A concrete encasement wa constructed to seal the well from sur face infiltration and to provide a bas for the traffic bearing access box. • A remote, metal -oxide semiconduc for (MOS) soil vapor sensor capabl of sensing many combustible and toxi gases, and organic vapors was it stalled in each soil vapor well. Tt- sensetr leads were sheathed in PV (Polyvinyl Chloride). and all conn tions were watertight. The On -Site Alarm System The alarm system consists of .Model LA Series LEAKALERT ar all the components. except the se/ sora• are housed inside a VEMA Tyl 4 enclosure. Each channel is ind pendently controlled with a single F board module. Each PC board equipped with a green LED power, indicator• and a red LED alarm ine Gator. Both LED indicators are visit from outside the electronics enclosut Each PC board is also equipped w- an alarm setpoint trimpot and a pu button switch to test the electronic c cult. Interfaces between the sense and the electronic control modules facilitated with FM -certified Zen safety barriers. The system is intri ically safe with operating voltages 3.5 volts. A two -channel strip ct recorder for monitoring the volt. output of each MOS sensor was stalled in order to obtain a hard cc of the leak detection system funeti Does It Work? A Leak Det` tion Event The leak detection system was a vated on September 11. 1984. On vember 12, 1984 a gasoline deliv 32 Hazardous Materials At Wa91e Management Magazine//uly•Aupu