LONG TERM 2 ENHANCED SURFACE WATER TREATMENT RULE

The LT2ESWTRLT2ESWTR:
  The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) is an EPA regulation targeting control of Cryptosporidium and other microbial contaminants.  It mandates treatment efficiency, i.e., log removal values, and gives credit to various treatment technologies to achieve the needed treatment efficiency. regulates 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. removal/inactivation in systems that use either a surface water or ground water under the direct influence of surface water (GWUDI)Ground water under the direct influence of surface water (GWUDI):
  Many groundwaters especially those in karst areas are recharged with significant amounts of surface water that does not pass through soil with its consequent filtering action but rather pass through sink holes directly into the groundwater.  A groundwater with significant amounts of insects, macroorganisms, algae, or microbials or sees rapid changes in turbidity, temperature or quality would most likely be considered a ground water under the direct influence of surface water..  The LT2ESWTR is long and complex and contains regulatory requirements for membrane processes for Cryptosporidium reduction, but it does not give specific removal credit which instead must be determined by testing. 

The LT2ESWTR lists several requirements for membranes.  First, membranes must meet the definition of a membrane which includes MFMicrofiltration (MF) membranes:
 Microfiltration membranes are typically hollow-fibers with a pore size range of approximately 0.1 – 0.2 μm (nominally 0.1 μm)., UFUltrafiltration (UF) membranes:
 Ultrafiltration membranes are typically hollow-fibers with a pore size range of approximately 0.01 – 0.05 μm (nominally 0.01 μm)., nanofiltration (NF)Nanofiltration (NF):
  Nanofiltration is a pressure driven membrane process that uses reverse osmosis to remove dissolved materials.  Nanofiltration applications are typically for softening or organics removal., reverse osmosis (RO)Reverse osmosis (RO):
  Reverse osmosis is the reverse of the natural osmosis process, i.e., the passage of a water through a semi-permeable membrane from a solution of higher concentration of dissolved solids to a solution of lower concentration.  Reverse osmosis applies a high pressure on the higher concentration side of the membrane to drive water through the membrane against the concentration gradient, in order to produce a water with a lower concentration of dissolved solids. and possibly cartridge filtrationCartridge filtration:
 Cartridge filtration uses disposable filter elements. The pore sizes can be the same as typical microfiltration membranes and the units could meet the definition of a membrane filter under the LT2ESWTR but often the pore sizes are much larger. systems as well as 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. and vacuum systemsVacuum 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 basic membrane definition is that particles larger than 1 µm are rejected by an engineered barrier primarily through size exclusion.  Secondly, the LT2ESWTR also requires that the removal efficiency of a target organism must be established through a challenge testChallenge testing:
 Challenge tests are conducted to determine the efficiency of removal of target particulates such as a microbe or a surrogate in order to calculate the log removal value of the membrane module. and direct integrityDirect 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. testing (40 CFR 141.2) and that the membrane “must undergo periodic direct integrity testing and continuous indirect integrity monitoringIndirect integrity monitoring:
 Indirect integrity monitoring consists of measuring some water quality parameter of the filtrate, e.g., turbidity or particle concentration, as an indicator of treatment effectiveness. during operation.”

The actual removal credit that a membrane receives is the lower of 1) “the removal efficiency demonstrated during challenge testing” or 2) “the maximum log removal valueLog 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 verified by the direct integrity test used to monitor the membrane filtration process”  (40 CFR 141.79(b)(1)).  Further information about challenge testing and direct integrity testing is included elsewhere in this educational module.  The LT2SWTR or the EPA Membrane Filtration Guidance Manual can also be consulted for the full in-depth information.  But briefly, challenge testing demonstrates the “ability of a membrane process to remove a target organism.”  Removal efficiency established by challenge testing sets the maximum removal credit that a membrane product can receive if this removal efficiency is not greater than that shown by direct integrity testing.  Direct integrity testing on the other hand addresses 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. that can occur during membrane operation which could allow microorganisms to pass.  Direct integrity testing is mandated for all membrane process in accordance w/LT2ESWTR (40 CFR 441.719(b)(3)) in order to “identify and isolate integrity breaches.”  The elements of direct integrity testing include:

Resolution: The test must be able to see a response from a 3 μm breach.

Sensitivity: The test must be able to verify log removal as approved by the state.

Frequency: The test must be able to be performed once per day unless the state grants less frequent testing.

Control limit:Control 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. A control limit must be established that triggers corrective action.

*Note that the unit typically has to be taken out of service temporarily for direct integrity testing.

The LT2ESWTR also mandates continuous indirect integrity monitoring since direct integrity testing is only conducted periodically (40 CFR 141.719(b)(4)22).  Continuous integrity monitoring must “continuously” monitor a filtrateFiltrate:
  Filtrate is the water that has passed through the membrane. water parameter that indicates removal of particulates with continuous defined as at least once every 15 minutes.  TurbidityTurbidity:
  Turbidity is a measure of  the cloudiness of a water as well as a gross measure of the amount of suspended solids in a water. is the default parameter measured in indirect integrity monitoring, but other parameters such as particle counting can be used.  A control limit must be established that will trigger immediate direct integrity testing if exceeded for more than 15 minutes.

EPA LT2ESWTR Guidance Manual