National Primary Drinking Water Standard’s Ground Water Rule

Thursday, January 01, 2009 - Written by Steve Cason, Wade Jackson, and Cary Jackson, Ph.D

Understanding the Requirements of the National Primary Drinking Water Standard’s Ground Water Rule

Part 2: Alternative Treatment Technologies and Compliance Monitoring

Steve Cason, Wade Jackson, and Cary Jackson, Ph.D†
Hach Company
5600 Lindbergh Drive
Loveland, Colorado 80539 USA

Introduction

The United States Environmental Protection Agency (USEPA) published the Ground Water Rule  (GWR) on November 08, 2006 with the intention of bringing systems that use ground water as a source to similar infrastructure and disinfection standards as the Surface Water Treatment Rule .  The requirements of the GWR apply to all Public Water Systems (PWSs), Community Water Systems (CWSs), and Non-community Water Systems (NCWSs) that use ground water sources, in whole or in part (including consecutive systems that receive finished ground water from another PWS), except where PWSs combine ground water with surface water or ground water under the direct influence of surface water (GWUDI) prior to treatment under the SWTR.

Specifically, the GWR establishes a risk-targeted approach to identify ground water systems that are susceptible to fecal contamination. The occurrence of fecal indicators in a drinking water supply is an indication of the potential presence of microbial pathogens that may pose a threat to public health. This Rule requires ground water systems that are at risk of fecal contamination to take corrective action to mitigate cases of illnesses and deaths due to exposure to microbial pathogens.  Corrective action includes changes to plant infrastructure, plant management, source water monitoring, disinfection treatment, and compliance monitoring.  Public Water System compliance with the GWR is scheduled for December 1, 2009.  This series of articles is intended to deconvolute the intricacies of the GWR that relates to fecal contamination and pathogen disinfection.

Part 2: Alternative Treatment Technologies and Compliance Monitoring

For a water system which has a significant deficiency as determined from the sanitary survey or a fecal indicator-positive ground water source sample, the GWS may be required to provide treatment that achieves at least 4-log removal of viruses or a State-approved combination of 4-log virus inactivation and removal before or at the first customer.  Technologies capable of providing at least 4-log treatment of viruses include the following:

  1. Inactivation, with a sufficient disinfection concentration and contact time with chlorine, chlorine dioxide, ozone, or through anodic oxidation.
  2. Removal with membrane technologies that have an absolute molecular weight cut-off (MWCO), or an alternative parameter that describes the exclusion characteristics of the membrane, that can reliably achieve at least 4-log removal of viruses
  3. Inactivation, removal or combination of inactivation and removal through alternative treatment technologies (e.g., UV radiation or in combination with chlorination and filtration) that can provide at least 4-log removal of viruses

Treatment by Chemical Disinfection

Chemical disinfection (chlorine, chlorine dioxide, ozone) technology is most popular in water treatment to achieve 4-log inactivation or removal of viruses.  The amount of chemical disinfection required to demonstrate 4-log inactivation becomes a function of disinfection demand, water temperature, hydrogen ion activity (pH), and contact time.  Contact tables (CT) published by USEPA are used to determine the chemical disinfectant dose required to achieve 4-log inactivation of viruses.

Ground water systems serving greater than 3,300 people and use chemical disinfection to provide 4-log inactivation must continuously monitor the residual disinfectant concentration using analytical methods specified in 40 CFR part 141.74(a)(2) at a location approved by the State.  The system must maintain the State-determined residual disinfectant concentration every day the GWS serves from the ground water source.  
Systems serving 3,300 people or fewer that use chemical disinfection must monitor the residual disinfectant concentration using analytical methods specified in 40 CFR part 141.74(a)(2) at a location approved by the State either by taking at least one grab sample every day the GWS serves water to the public or by continuously monitoring the disinfectant residual.

Systems that use continuous monitoring must record the lowest residual disinfectant level each day that the GWS is in service.  If the system fails to maintain the State-specified disinfectant residual level necessary to achieve 4-log inactivation of viruses, the GWS must restore the State-specified residual disinfectant level within four hours.  If the continuous monitoring equipment fails, the GWS is required to collect and measure a grab sample every four hours until the equipment is back on-line.  The system has 14 days to resume continuous monitoring.  

If a GWS collecting grab samples has a disinfectant residual below the State-specified disinfectant residual concentration, the system must collect and measure disinfectant residual every four hours until the minimum disinfectant residual is restored.  Failure to restore the minimum disinfectant residual to the required 4-log inactivation of viruses, using either grab sampling and subsequent analysis or continuous monitoring is a treatment technique violation, subject to fines.
 
Treatment by Membrane Filtration


Membrane filtration systems achieve 4-log removal of viruses when the MWCO (200-400 Daltons) is sufficient to reject 0.5 nm particles.  The MWCO must be determined for specific membrane to meet these conditions as not all membranes have the same specificity.  However, regardless of the membranes MWCO, membrane filtration treatment alone does not provide disinfection residual to address potential post treatment contamination in the water distribution system.

Ground water systems that use membrane filtration treatment technology for 4-log removal of viruses must maintain the integrity of the membrane and monitor and operate the system in accordance with State-specified monitoring and compliance requirements.  If a system fails to meet these requires, it must correct the problem within four hours or be in treatment violation, also subject to fines.

Ultraviolet radiation (UV) treatment technology is inefficient in inactivation of certain viruses and therefore is not an acceptable stand alone treatment technology.  However, the USEPA is allowing its use in combination with other approved treatment technologies.

Treatment by Alternative Technologies

To enhance 4-log removal of viruses or to mitigate post disinfection treatment contamination in the water distribution system, GWS may apply alternative treatment technologies that include membrane filtration and UV in combination with chemical disinfection treatment.  Systems that use a State-approved alternative treatment technology must monitor and operate the technology in accordance with all compliance requirements to adequately demonstrate that at least 4-log treatment of viruses is achieved.  Should the GWS fail to demonstrate at least 4-log removal of viruses, the GWS must restore proper operation with 4 hours or be in treatment violation and subject to fines.

Continuous Disinfection Residual Monitoring Technologies

The next and final article (Part 3) in this series on Understanding the Requirements of the National Primary Drinking Water Standard’s Ground Water Rule takes a look at the approved technology used for disinfectant residual compliance monitoring and compares it to amperometric chlorine probes currently under approval consideration by USEPA.  Side-by-side data comparison of the approved DPD pump system with free and total amperometric chlorine probes will be compared and contrasted for regulatory reporting purposes.


† To whom correspondence should be addressed
  1 Federal Register / Vol. 71, No. 216 / Wednesday, November 8, 2006 / Rules and Regulations
2  Federal Register / Vol. 63, No. 241 / Wednesday, December 16, 1998 / Rules and Regulations