DIRECT INTEGRITY TESTING REQUIREMENTS OF THE LT2ESWTR (40 CFR 141.719(b)(2))

Systems must conduct direct integrity testingDirect integrity test:
A direct integrity test refers to the process usually performed daily to detect breaches in the membrane system.  Integrity tests are pressure-based or marker-based. in a manner that demonstrates a removal efficiency equal to or greater than the removal credit awarded to the membrane filtration process and meets the requirements described in paragraphs (b)(3)(i) through (vi) of this section. A direct integrity test is defined as a physical test applied to a membrane unit in order to identify and isolate integrity breachesIntegrity breach:
  A breach refers to leakage in the membrane module due to a broken fiber, leaking seal or other leak that can allow microbes and particulates to bypass the membrane and pass directly into the finished water. (i.e., one or more leaks that could result in contamination of the filtrateFiltrate:
  Filtrate is the water that has passed through the membrane.).

(i) The direct integrity test must be independently applied to each membrane unit in service. A membrane unit is defined as a group of membrane modules that share common valving that allows the unit to be isolated from the rest of the system for the purpose of integrity testing or other maintenance.

(ii) The direct integrity method must have a resolution of 3 micrometers or less, where resolution is defined as the size of the smallest integrity breach that contributes to a response from the direct integrity test.

(iii) The direct integrity test must have a sensitivity sufficient to verify the log treatment credit awarded to the membrane filtration process by the State, where sensitivity is defined as the maximum log removal value (LRV)Log removal value (LRV) or log reduction credit:
  The log removal value or log removal credit is the filtration removal efficiency for a target organism, particulate, or surrogate expressed as log₁₀(feed concentration) – log₁₀(filtrate concentration). that can be reliably verified by a direct integrity test. Sensitivity must be determined using the approach in either paragraph (b)(3)(iii)(A) or (B) of this section as applicable to the type of direct integrity test the system uses.

(A) For direct integrity tests that use an applied pressurePressure system:
  A pressure membrane system applies a pressure to the feed water side of the membrane in order to force the water through the membrane. or vacuumVacuum systems:
  Vacuum membrane systems are microfiltration or ultrafiltration systems in which the membranes are immersed in a tank of water and a vacuum applied to pull the water through the membrane., the direct integrity test sensitivity must be calculated according to the following equation:

LRV_DIT = Log₁₀(Q_p/(VCF × Q_breach))     Equation 1

Where:

LRV_DIT = the sensitivity of the direct integrity test

Q_p = total design filtrate flow from the membrane unit

Q_breach = flow of water from an integrity breach associated with the smallest integrity test response that can be reliably measured

VCF = volumetric concentration factor

The volumetric concentration factor is the ratio of the suspended solids concentration on the high pressure side of the membrane relative to that in the feed waterFeed water:
 The feed water is the water stream applied to the membrane unit..

(B) For direct integrity tests that use a particulate or molecular marker, the direct integrity test sensitivity must be calculated according to the following equation:

LRV_DIT = Log₁₀(C_f) - Log₁₀(C_p)     Equation 2

Where:

LRV_DIT = the sensitivity of the direct integrity test

C_f = the typical feed concentration of the marker used in the test

C_p = the filtrate concentration of the marker from an integral membrane unit.

(iv) Systems must establish a control limitControl limit (CL):
 A control limit in membrane systems refers to a response from an integrity test, for example exceeding a maximum allowable rate of pressure loss, that triggers a response by the operators such as searching for breaches. within the sensitivity limits of the direct integrity test that is indicative of an integral membrane unit capable of meeting the removal credit awarded by the State.

(v) If the result of a direct integrity test exceeds the control limit established under paragraph (b)(3)(iv) of this section, the system must remove the membrane unit from service. Systems must conduct a direct integrity test to verify any repairs, and may return the membrane unit to service only if the direct integrity test is within the established control limit.

(vi) Systems must conduct direct integrity testing on each membrane unit at a frequency of not less than once each day that the membrane unit is in operation. The State may approve less frequent testing, based on demonstrated process reliability, the use of multiple barriers effective for CryptosporidiumCryptosporidium:
 According to the U.S. Center for Disease Control, Cryptosporidium is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as "Crypto." There are many species of Cryptosporidium that infect humans and animals. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very tolerant to chlorine disinfection. While this parasite can be spread in several different ways, water (drinking water and recreational water) is the most common method of transmission. Cryptosporidium is one of the most frequent causes of waterborne disease among humans in the United States., or reliable process safeguards.