Number of Wells that Tested Positive for Total Coliform Bacteria – A total of 7,035 (13%) of 51,028 wells tested were positive for total coliform bacteria. This was not considered a “failure”, but these wells were then required to do follow-up testing for fecal coliform or E. coli. The NJDEP believes that a significant percentage of wells testing positive for total coliform are not actually contaminated with fecal waste. Some coliform of non-fecal origin may be present as buildup in the plumbing system, for example. Number of Wells that Tested Positive for Fecal Coliform or E. coli – A total of 1136 ( 2 . 2 % ) o f t h e 5 1 , 0 2 8 w e l l s t h a t w e r e s a m p l e d w e r e p o s i t i v e f o r e i t h e r f e c a l c o l i f o r m or E. coli in at least one of the samples collected at the well. presented by county in Appendix E. These data are
Geographic Distribution – The percentage of wells with fecal coliform or E. coli in the combined counties above Burlington and Monmouth (“northern”) was 3.5%. In the remaining (“southern”) counties, the percentage was 1.0% (see Figure 3 above). The NJDEP believes the northern/southern difference is real and not an artifact of the use of different labs or different methods in these two regions. Both laboratory and method biases exist but do not account for the observed difference between the northern and southern parts of the state. The difference is most likely due to the different geology in these regions. The geology in the north is characterized by areas with limestone subject to solution cavities (called karst), fractured bedrock and gravel/cobble water-bearing zones. The southern part of the state is comprised
mainly of the coastal plain (alternating layers geology appears to protect ground water from
of sand and clay). fecal contamination
Coastal plain better than the
other geological areas of the state. Comments – The percentage of wells coliform or E. coli after the two years
testing positive for total coliform of PWTA testing, when the data
and fecal were first
analyzed, was 13% and 2.1%, respectively (compared to between September 2002 – April 2007, respectively).
13% and 2.2% failure rate Thus, the percentages of
wells testing positive are consistent following the
testing in the
of an extent
additional 24,964 of fecal pollution
impact, the percentages found in this any significant extent in the future.
For the bacteriological analysis, the data are based on a single sample in 91% of the cases.7 Thus, the 2.2% fecal coliform/E. coli -positive figure should be considered a
lower limit of the true extent of microbes are randomly distributed
fecal contamination in New in ground water and because
Jersey. Because fecal contamination
can often be low or intermittent, a single sample can miss the Alternately, fecal contamination may be present in some samples in
contamination. the absence of
coliform bacteria8. A reasonable statewide is perhaps an additional
estimate of the true one or two percent.
7 Test results are valid for 6 months. For homes that sold more than once during this four and half year period, or did not sell within a 6-month period, the well was tested more than once. The 51,035 wells included 4,431 with multiple t e s t r e s u l t s ( 9 3 . 3 % o f t h o s e w e r e t e s t e d t w i c e ; 6 . 1 % w e r e t e s t e d 3 t i m e s ; a n d 0 . 5 % w e r e t e s t e d m o r e t h a n 3 t i m e s . ) 8 Atherholt, T. et al. October 2003. Evaluation of Indicators of Fecal Contamination in Ground Water. American Water Works Association. 95 (10): 119. Journal