There are two parts of the permit that call for water quality monitoring. One requires wet weather monitoring of all outfalls that discharge directly to any stormwater impaired waters to determine what areas are contributing to the impairment. This requirement is detailed on pages 41-44 of the MS4 permit.
The other monitoring requirement is part of tracking down illicit discharges to the MS4 via the IDDE program. See pages 7-11 in Appendix B of the permit for details.
Wet weather monitoring: means sampling an outfall during or after any rainfall event that results in a discharge from the outfall.
Dry weather monitoring: means sampling an outfall only when no more than 0.1 inches of rainfall has occurred in the previous 24 hours.
Stormwater impaired waters: means a subset of the surface waters of the state identifed as impaired in the most recent Connecticut Integrated Water Quality Report as a result of stormwater runoff. See the MS4 Map Viewer for a map layer of CT's stormwater impaired waterbodies.
This chart outlines the key elements of the two main monitoring requirements in the MS4 general pemit: Impaired waters monitoring and IDDE monitoring. IDDE monitoring requirements are split into two sections: Baseline monitoring and the Catchment Investigation Procedure.
We compiled example monitoring equipment that may be used to meet permit requirements and included costs for both in-house test kit/portable meter sampling vs. laboratory services. We've also created a map of the certified labs towns can use to analyze samples for bacteria, total N and total P.
NOTE: Bacteria sampling can’t be done in the field so requires lab services.
| Pollutant | Test Kit/Meter | Price | Samples per kit | Cost per sample | Comments | Commercial lab cost per sample (estimate) |
|---|---|---|---|---|---|---|
| Ammonia | Hach N1-8 | $88 | 100 | $0.88 | Reagent for this kit contains mercury | $9.00 |
| Surfactants | Hach DE-2 | $307 | 32 | $9.59 | $16.00 | |
| Chlorine | Hach CN-66F Quantofix Chlorine test strips |
$55 $31 |
100 100 |
$0.55 $0.31 |
Sampling for either free chlorine or total chlorine is acceptable. DEEP is looking for detectable chlorine and the test kits or strips should have a lower detection limit of 0.1 mg/l or less. | $3.00 |
| Turbidity | Hach 2100Q | $1180 | n/a | TBD | ||
| LaMotte 2020we | $980 | n/a | ||||
| HF Scientific MicroTPW | $799 | n/a | ||||
| Nitrogen, phosphorus | Lamotte Smart3 (Requires Heater Block for TN/TP) | $999 + $779 (heater block) = $1778 | $123 (TN) $89(TP) |
$4.90 (TN) $7.56 (TP) |
|
$8 (TP) $23 (TN) |
Monitoring of stormwater outfalls is required under the new MS4 permit, however the approach is slightly different than under the 2004 permit.
Now, all MS4 outfalls that discharge directly to stormwater impaired waters should be sampled at least once during the 5-year term of the permit. Visit our MS4 Map viewer to find out what waters in your town are impaired by stormwater. Note that all MS4 outfalls must be inventoried and mapped as part of the IDDE requirements but for this requirement, those outfalls that discharge to stormwater impaired waters must also be sampled for that impairement.
If you already have wet weather sampling data, it can be used to meet this requirement.
| Pollutant of Concern | Screening threshold |
|---|---|
Nitrogen |
Total nitrogen > 2.5 mg/l |
Phosphorus |
Total phosphorus > 0.3 mg/l |
Bacteria |
For discharges to Class AA, A, and B surface waters: |
Other pollutant of concern |
Turbidity 5 NTU greater than instream sample just upstream of outfall |
Before you begin the dry weather sampling requirements in the IDDE section, each MS4 must develop an inventory of all outfalls in priority areas, sort those outfalls into 4 categories (problem, high priority, low priority, excluded), and rank all the outfalls in each category based on specific characteristics. See the IDDE implementation section of this website or Appendix B of the permit for more details.
The IDDE section requires dry weather sampling of outfalls in priority areas that are classified as high or low priority (it does NOT need to be done for catchments in priority areas that are classified as problem or excluded outfalls). Dry and wet weather sampling is to be used as part of the follow-up investigations to help identify where an illicit discharge is coming from.
All the dry and wet weather samples may be done with test kits or meters (except bacteria) and need to be analyzed for the constituents listed below. Proper sampling procedures need to be followed - for more information, there's a recording of the IDDE Dry weather screening and sampling presentation given at the IDDE workshop on the IDDE page. Also, see EPA's guide to proper sampling procedures.
*Note that no test kits exist for total nitrogen or total phosphorus - these samples will likely need to be sent to a laboratory.
Samples that exceed any of the following criteria shall be ranked at the top of the High Priority catchments for further investigation:
Example spreadsheet for collecting required data during water quality sampling.
And an example fieldwork checklist used for water quality monitoring at the UConn Storrs campus.
Most requirements for this section are in effect as of July 1, 2017 for all MS4s but more time is provided for the legal authority component.
Where the deadline for new MS4 permittees differs from the deadline for exisiting permittees, the second deadline in parenthesis applies to new permittees.
| Activity | Deadline | Permit Page |
|---|---|---|
Impaired Waters Monitoring |
||
Complete inventory of all outfalls that discharge to impaired waters |
Jul 1 2019 (Jul 1 2020) |
43 |
Begin screening outfalls to impaired waters |
Jul 1 2018 |
44 |
Complete screening 50% of outfalls to impaired waters |
Jul 1 2020 (Jul 1 2021) |
44 |
Complete screening all outfalls to impaired waters |
Jul 1 2022 |
44 |
Begin follow-up investigations where needed |
Jul 1 2019 (Jul 1 2020) |
44 |
Begin to monitor 6 'worst' outfalls annually |
Jul 1 2020 (Jul 1 2021) |
44 |
IDDE Monitoring |
||
Complete dry weather sampling (of all MS4 outfalls in High & Low priority catchments) |
Jul 1 2020 (Jul 1 2022) |
Appendix B p.12 |
Conduct wet weather sampling where required as part of Catchment Investigation Procedure |
No specific deadline |
Appendix B p.10 |
The NEMO program presented a workshop on the CT MS4 water quality monitoring requirements on June 20, 2019 at Milford City Hall. Most of the presentations were recorded. The presentation slides and recordings (where available) can be found below.
