Ground Water Under Direct Influence of Surface Water (GWUDI)
July 14,2016
the staff of the Ridgewood blog
Ridgewood NJ, The term “GWUDI” refers to a groundwater source that is located close enough to nearby surface water (e.g., a river or lake) so as to receive some amount of direct surface water recharge. If a portion of the water source is from surface water, then the groundwater source is considered to be at risk of contamination from pathogens and viruses that are not normally found in true groundwater. Ridgewood completed a screening process of all of its wells in 1994, and the New Jersey Department of Environmental Protection (NJDEP) found that none of the wells were considered to be under the direct influence of surface water.
More recently, data reviewed by the U.S. Environmental Protection Agency (EPA) suggested that five Ridgewood Water wells may be under the direct influence of surface water, and as a result, Ridgewood Water has installed advanced disinfection equipment at four of these locations, and removed the fifth well from service. Ridgewood Water will continue to study the water quality at these wells during the next year to better understand the relationship between surface water and groundwater and determine whether additional treatment steps are necessary.
In light of this information, Ridgewood Water is also performing a study of 33 additional wells in the water supply system that are located near surface water bodies to look for any evidence of surface water influence in these wells. If any evidence is found during the course of this study of such a connection, Ridgewood Water will immediately install advanced disinfection treatment at these locations. It is important to note that routine distribution system monitoring of the Ridgewood Water distribution system since 2005 has never detected any positive samples in the entire system that would indicate a surface water impact on microbiologic quality of water supplied to customers.
Ridgewood Water is beginning a year-long study of its supply well system to evaluate the vulnerability of the wells to microbiological contamination from nearby surface water bodies.
Quarterly progress updates can be found HERE.
ABOUT THE STUDY
Ridgewood will be performing the GWUDI study under a rigorous Source Water Monitoring Plan which has been approved by the EPA. The study involves the collection of water samples from up to 38 wells and three surface water locations on a weekly and biweekly basis. The samples will be analyzed in the laboratory for evidence of microbiologic activity and for other “indicator parameters” that may indicate surface water influence.
All samples will be collected and analyzed by an NJDEP-certified laboratory and will be reported on a quarterly basis to the NJDEP and EPA.
Group 1 Wells (2 locations)
For the two Group 1 wells, EPA has determined that the occasional presence of of e.coli in raw water has occurred and is requiring further assessment to determine whether there is evidence of a direct connection of these sources to surface water. Ridgewood will perform weekly raw water monitoring at the two Group 1 wells for the presence of fecal coliform, e. coli and turbidity.
Group 2 Wells– (3 locations)
For the three Group 2 wells, EPA has determined that the occasional presence of of e.coli in raw water has occurred and is requiring further assessment to determine the degree of influence of nearby surface water on each well and whether there is a need for additional treatment. Ridgewood will perform weekly raw water monitoring at the two Group 2 wells for the presence of fecal coliform, e. coli, aerobic spores, pH, temperature and turbidity. Ridgewood will also perform weekly surface water monitoring at associated surface water bodies for the same parameters. The third well has been shut down and is being reevaluated for reconstruction or permanent closure.
Group 3 Wells – (33 locations)
The 33 Group 3 wells have not exhibited any evidence of being under the influence of surface water. These wells were previously screened by NJDEP and were not found to warrant additional assessment. As such, the NJDEP issued monitoring waivers to Ridgewood for these wells. EPA has determined that a further assessment of these wells is warranted at this time. The monitoring will consist of biweekly raw water sampling and analysis for e.coli bacteria.
Ridgewood has also agreed to perform Hydrogeologic Sensitivity Assessments (HSAs) of all Group 3 wells. These are reviews of the conditions and potential sources of surface contamination at each location to assess their vulnerability to future microbiologic contamination
