Nitrate and nitrite
Norwalk City
Nitrate and nitrite enter water from fertilizer runoff, septic tanks and urban runoff. These contaminants can cause oxygen deprivation for infants and increase the risk of cancer. Nitrite is significantly more toxic than nitrate. Click here to read more about nitrate.
70
Samples
0
Samples exceeding legal limit (MCL)
55
Samples exceeding
health guidelines
Testing results - average by year
| Year | Average result | Samples taken | Detections | Range of results |
|---|---|---|---|---|
| 2014 | 0.544 ppm | 12 | 12 | 0.240 ppm - 1.10 ppm |
| 2015 | 0.511 ppm | 12 | 10 | ND - 1.14 ppm |
| 2016 | 0.250 ppm | 12 | 5 | ND - 0.810 ppm |
| 2017 | 0.313 ppm | 12 | 7 | ND - 0.840 ppm |
| 2018 | 0.374 ppm | 12 | 11 | ND - 0.790 ppm |
| 2019 | 0.490 ppm | 10 | 10 | 0.170 ppm - 0.820 ppm |
ppm = parts per million
State and national drinking water standards and health guidelines
EWG Health Guideline 0.14 ppm
The health guideline of 0.14 parts per million, or ppm, for nitrate and nitrite is based on the equivalent health guideline for nitrate, as defined in a peer-reviewed scientific study by EWG. This guideline represents a one-in-one-million annual cancer risk level.
EPA Maximum Contaminant
Level (MCL) 10 ppm
ppm = parts per million
All test results
| Date | Lab ID | Result |
|---|---|---|
| 2014-01-15 | AG62884 | 0.610 ppm |
| 2014-02-12 | AG64524 | 0.730 ppm |
| 2014-03-05 | AG65768 | 0.780 ppm |
| 2014-04-02 | AG67508 | 0.770 ppm |
| 2014-05-07 | AG70041 | 1.10 ppm |
| 2014-06-04 | AG72190 | 0.280 ppm |
| 2014-07-02 | AG74561 | 0.240 ppm |
| 2014-08-06 | AG77082 | 0.730 ppm |
| 2014-09-03 | AG79537 | 0.450 ppm |
| 2014-10-08 | AG82469 | 0.280 ppm |
| 2014-11-05 | AG84394 | 0.250 ppm |
| 2014-12-03 | AG86460 | 0.310 ppm |
| 2015-01-07 | AG88645 | 0.270 ppm |
| 2015-02-04 | AG90153 | 0.600 ppm |
| 2015-03-04 | AG91760 | 0.980 ppm |
| 2015-04-01 | AG93591 | 1.14 ppm |
| 2015-05-13 | AG96407 | 0.710 ppm |
| 2015-06-03 | AG97778 | 0.710 ppm |
| 2015-07-08 | AH00610 | 0.710 ppm |
| 2015-08-05 | AH02699 | 0.250 ppm |
| 2015-09-02 | AH04987 | 0.350 ppm |
| 2015-10-07 | AH07447 | 0.410 ppm |
| 2015-11-04 | AH09317 | ND |
| 2015-12-02 | AH11125 | ND |
| 2016-01-06 | AH13089 | ND |
| 2016-02-03 | AH14724 | 0.470 ppm |
| 2016-03-02 | AH16437 | 0.810 ppm |
| 2016-04-06 | AH18799 | 0.700 ppm |
| 2016-05-04 | AH20801 | 0.560 ppm |
| 2016-06-08 | AH23381 | 0.460 ppm |
| 2016-07-13 | AH25927 | ND |
| 2016-08-03 | AH27389 | ND |
| 2016-09-07 | AH30110 | ND |
| 2016-10-05 | AH32792 | ND |
| 2016-11-02 | AH34981 | ND |
| 2016-12-07 | AH37625 | ND |
| 2017-01-11 | AH40302 | ND |
| 2017-02-01 | AH42069 | 0.410 ppm |
| 2017-03-01 | AH44130 | 0.800 ppm |
| 2017-04-05 | AH46503 | 0.790 ppm |
| 2017-05-03 | AH48833 | 0.840 ppm |
| 2017-06-07 | AH51408 | 0.330 ppm |
| 2017-07-05 | AH53781 | 0.210 ppm |
| 2017-08-02 | AH56154 | ND |
| 2017-09-06 | AH59049 | ND |
| 2017-10-04 | AH61408 | ND |
| 2017-11-08 | AH63906 | ND |
| 2017-12-06 | AH65866 | 0.380 ppm |
| 2018-01-03 | AH67429 | 0.240 ppm |
| 2018-02-14 | AH70126 | 0.790 ppm |
| 2018-03-06 | 18-13863-02 | 0.680 ppm |
| 2018-04-02 | 18-16500-04 | 0.550 ppm |
| 2018-05-01 | 18-17865-04 | 0.420 ppm |
| 2018-06-05 | 18-20677-06 | 0.420 ppm |
| 2018-07-10 | 18-23938-05 | ND |
| 2018-08-07 | 18-26412-04A | 0.170 ppm |
| 2018-09-04 | 18-28827-04A | 0.150 ppm |
| 2018-10-02 | 18-31424-05 | 0.300 ppm |
| 2018-11-06 | 18-341590-5 | 0.300 ppm |
| 2018-12-03 | 18-36103-05 | 0.470 ppm |
| 2019-01-07 | 19-10552-04A | 0.550 ppm |
| 2019-02-04 | 19-12317-04 | 0.820 ppm |
| 2019-03-04 | 19-14221-05 | 0.740 ppm |
| 2019-04-02 | 19-16345-04A | 0.630 ppm |
| 2019-05-06 | 19-19014-04A | 0.500 ppm |
| 2019-06-04 | 19-21157-05 | 0.390 ppm |
| 2019-07-01 | 19-23872-04A | 0.570 ppm |
| 2019-08-07 | 19-27050-04 | 0.170 ppm |
| 2019-09-03 | 19-29348-04A | 0.300 ppm |
| 2019-10-01 | 19-31924-04A | 0.230 ppm |