Ground Water Rule

The Ground Water Rule (GWR) was developed to provide for increased protection against fecal contamination in public water systems that use groundwater sources. This regulation also affects systems that do not have their own sources but are served by other groundwater systems. The GWR establishes a risk-targeted approach for groundwater systems that may be susceptible to fecal contamination. The occurrence of fecal indicators in a drinking water supply is an indication of the potential presence of microbial pathogens (disease causing organisms) that may pose a threat to public health. This rule requires groundwater systems that are at risk of fecal contamination to take corrective action to reduce possible cases of illnesses due to exposure to microbial pathogens.

This rule includes community and non-community systems that use groundwater sources. Groundwater sources include wells, springs, galleries, and any other water sources that are not regulated under the Surface Water Treatment Rule. Systems must comply with the requirements of the GWR beginning December 1, 2009.

There are three major areas of concern for your system-

Sanitary Surveys

When inspections are done at your system, a more thorough investigation will be performed than has been done in the past. Surveys will cover the following areas-

Sources Distribution system
Finished water storage Pumps, pump facilities, and controls
Treatment Monitoring, reporting, and data verification
System management and operation Operator compliance with State requirements

After the completion of the survey, you will be provided with a report within 30 days. Any significant deficiencies will have to be corrected within 120 days. In lieu of correction completion, the system will need to submit a schedule for the correction of these deficiencies within 120 days. Water systems will be provided with a list of significant deficiencies that we will look for at a later date.


Anytime your system submits a routine Revised Total Coliform Rule (RTCR) sample that is positive after December 1, 2009, you will submit a sample from each of your groundwater sources that were in use at the time of the positive RTCR sample. The triggered samples must be taken within 24 hours of receiving the results of the positive RTCR sample. One triggered sample must be submitted from each source for each positive routine RTCR sample. This is in addition to your normal "repeat" samples taken in the distribution system. This follow-up source sampling is referred to as triggered sampling as it has been triggered by the positive RTCR sample. This sampling will be done to determine if the cause of the contamination is from a distribution system problem or a source water problem. These triggered source samples will be analyzed in a manner similar to the RTCR samples. If they are E. coli positive, five more source samples will be submitted. If any of these five repeat triggered samples are E. coli positive, your system will have to take corrective action to remedy the problem with the contaminated source. Any triggered samples should be marked as "GWR" on the sample submission forms. These are not "routine" or "repeat" samples as these samples types are for compliance with the RTCR. Some systems may have to install sampling taps on their wells to be able to take these samples.

Please note that when you do triggered sampling, you must sample every source that was in use at the time of the positive RTCR sample. If you have a large number of sources, you may want to submit a plan to sample a representative number of sources rather than all sources. This plan would have to be approved prior to its use.

For systems that are served by another groundwater system (such as a rural water system), you will need to notify your water supplier about your positive RTCR sample within 24 hours, and they will have to submit the triggered samples from their source(s).

The triggered sampling applies to any groundwater system that does not treat its groundwater to a level of 4 log inactivation thru chlorination or some other means. If you would like to demonstrate that you treat to this level, please contact me for further information.

The Drinking Water Program will also determine if there are some water systems with sources that we feel are extremely susceptible to contamination based on the local hydrology such as drawing water from a shallow aquifer. These sources will submit monthly source samples for a year to determine their vulnerability. Positive E. coli source samples could lead to corrective actions for these systems. Systems will be notified if they need to conduct this assessment monitoring.

Corrective Actions

Systems with sanitary survey deficiencies or with E. coli positive source samples (either triggered or assessment samples) will need to take corrective actions. These actions can include-

  • Correct all sanitary survey deficiencies
  • Provide an alternate source of water
  • Eliminate the groundwater source of contamination
  • Install treatment for the contaminated groundwater source

The simplest method of treatment would be the installation of a disinfectant (usually chlorine) with a proper length of contact time before the first customer. Monitoring of chlorine levels would also then be required. It should be noted that just because you are currently chlorinating does not mean you are in compliance with this section of the rule. You must have the proper amount of contact time and the proper level of disinfectant to inactivate viruses to be in compliance. This is known as a "4 log inactivation" of viruses.

More information can be found on the EPA Groundwater web site

A slide presentation on the Ground Water Rule can be found here (GWR.pdf)

A spreadsheet to calculate 4 log inactivation can be found here (SD GWR CT.xls)

More information on the Ground Water Rule can be found by contacting Barb Friedeman in the Drinking Water Program at (605) 773-3754.