Secondary Containment Sump Testing with as little as 2 inches of water

assembled sensor

Some state and local regulations require all secondary containment sumps, dispenser pans and spill buckets to be tested for leaks every three years.  New systems are to be tested upon installation, 6 months after, and then every 3 years in some areas.  Complying with these new regulations can be time-consuming and expensive. 

These regulations have not specified what kind of test must be performed, operators have to show that the sumps are functioning to the manufacturer specifications which in many cases has been a 24-hour hydrostatic test, water level change less than ¼ inch.  This can mean long and costly shutdowns of tanks and dispensers.  Regulations will allow alternative faster methods if they are at least as accurate. Sensor is approximately 2.5 inches in diameter and various lengths.  Short version works in as low as 2 inches of water in sump.                         

Faster Testing and Lower Cost

The patented Caldwell Level Change Indicator provides fast, accurate hydrostatic testing.  It is designed to show hydrostatic water level changes on the order of + or – 0.0025 inches.  This high degree of resolution allows for accurate testing in a minimal amount of time. 

Fast test time not only gets your sites up and running faster, it eliminates any problems associated with evaporation.  In dry climates, evaporation over a 24-hour period can exceed the leak rate you are trying to detect.


For example, movement of the float indicator one circle in one hour is the equivalent of the manufacturer’s specs of 0.25 inch level change in a 24-hour test period. Our system can achieve the same accuracy in a 30 minute test if the indicator moves ½ circle or more.

The simple operation and low price of the Level Change Indicator means you can have several indicators running at one time.  Get in and out of a site quickly and maximize your profits while minimizing your labor. The design is all mechanical and requires no electrical hookups.                           

Principles of Operation

Assemble the support board and pass the float bead chain through fine adjustment hollow tube and attach to sensor bail. Position support board along one edge of the containment sump and Lower the sensor slowly down to water level until the float black indicator moves to the center of the scale. Lock chain in slot of hollow tube and rotate fine adjustment nut to move float position indicator to first circle then start test.


All testing should start at first circle and any movement passed the next circle in one hour is a change of at least 0.01 inches or in many cases a possible leak according to manufacturer’s guidelines. Overfill buckets and other small containment sumps may require a larger level change for a given leak rate since the surface area is small. If the sump is tight there will be little or no visible movement of the indicator over the test duration. The user is to apply measured level change rate to regulations to determine if sump is tight.


If liquid level is decreasing over time, float indicator will move outward. A level change from the first circle to the 2nd and 3rd circles represents a level change of approximately 0.01 inches each.  It is easy to see a change of about 1/4 a circle and this would represent a 0.0025 inch level change over the time period of the test. This high degree of resolution meets all regulation requirements.


The actual leak rate depends on surface area of the water in the sump. Calculate this area in square inches and divide by 231 to get gallons/inch level change. Divide this by 100 to get volume change for each circle the float moves. If this volume change is over a 1 hour test time then it represents leak rate in gallons per hour. If test time is 30 minutes multiply by 2 for leak rate in gallons per hour.