Learn how to tell dissolved from particulate lead with paired samples, cut sources through housekeeping, and choose dissolved-metal media when an MSGP lead benchmark exceedance triggers AIM.
Under the 2021 MSGP, a lead benchmark exceedance triggers Additional Implementation Measures (AIM), which means you review your controls and respond before any treatment decision. The sequence that works is to confirm whether the lead is dissolved or particulate with paired samples, cut the sources through housekeeping, and add dissolved-metal media where sediment controls leave the dissolved fraction behind.
What is the MSGP benchmark for lead, and what does an exceedance require?
The lead benchmark depends on hardness, so you find your number in the hardness table in Appendix J of the 2021 MSGP. For sectors that sample a hardness-dependent metal, EPA includes hardness ranges, and you collect hardness data on your receiving water to pick the range. You only need hardness for discharges to freshwater, because the metal benchmarks do not vary for saline waters.
AIM is triggered by a benchmark exceedance, which can occur two ways, according to EPA's ECHO summary of AIM data. One is an exceedance of the four-quarterly annual average. The other applies when you have fewer than four quarterly samples and the sum of sample results in the sample year exceeds the benchmark by more than four times, which indicates the annual average would be exceeded anyway. In practice, a single very high lead result can put you in AIM early.
Is the 2026 permit going to change this?
It may, depending on your sector. EPA's proposed 2026 MSGP fact sheet describes shifting certain sectors from indicator or report-only monitoring to benchmark monitoring for pH, TSS and chemical oxygen demand, and adding new benchmark monitoring for ammonia, nitrate, nitrite and metals. The fact sheet lists the affected sectors in a summary table. Check your sector there, and review the final permit text when EPA issues it.
Where does dissolved lead come from on an industrial site?
Lead reaches runoff from vehicle-related deposition, metal fines and slag, and corroding scrap or stock. A USGS study of urban stormwater in Maricopa County, Arizona found that lead, cadmium, zinc and ammonia are released by urban activities and accumulate in bed material, and it attributed the lead probably to vehicles that use leaded gasoline. That is a regional finding, but it shows why paved, vehicle-heavy areas deserve a look.
Grinding, cutting and welding leave metal fines and slag on pavement that wash toward catch basins with each rain. Those fines start as particles, then corrode and break down into dissolved ions. The table below pairs each source with its likely form and the first control to apply. The forms reflect general chemistry and will vary by site.
| Source | Likely form | First control |
|---|---|---|
| Vehicle deposition on paved lanes | Particulate, partly dissolved | Sweeping, inlet protection |
| Metal fines and slag from cutting or grinding | Particulate that corrodes to dissolved | Vacuum sweeping, covered work areas |
| Corroding scrap or stock stored outside | Dissolved and particulate | Cover or move under roof |
| Batteries or lead-bearing parts | Dissolved after leaching | Containment, covered storage |
How do pH, hardness and organic carbon affect dissolved lead?
Lower pH and organic carbon keep lead in solution, while higher pH and abundant particles pull it onto solids. This is general water chemistry rather than a site-specific rule. Acidic runoff, such as water running off corroding stock, holds more lead as free ions. Dissolved organic carbon binds lead into complexes that pass through a filter and count as dissolved. Suspended solids give lead surfaces to attach to, so sediment-rich runoff tends to carry a larger particulate share.
Hardness matters twice. Calcium and magnesium compete with lead for binding sites, and hardness also moves your benchmark number. Record pH, hardness and organic carbon with every lead sample so you can interpret the result.
Is my exceedance dissolved or particulate?
Compare total and dissolved lead in paired samples from the same storm and location. If the dissolved result is a large share of the total, the lead is mostly dissolved and sediment controls alone will not fix it. If dissolved lead is small and total lead tracks your TSS, the problem is particulate.
Use this decision rule:
- Dissolved is a small share of total: put your effort into sediment control and housekeeping.
- Dissolved is a large share of total: add dissolved-metal media, since TSS controls capture particulate matter but not dissolved ions.
- Both fractions are substantial: combine sediment control with dissolved-metal media.
How should I sample for lead?
Collect samples during storm events, as grab or composite samples, using EPA's industrial stormwater monitoring guide as the baseline. It describes quarterly visual assessments of a storm-event grab sample, checking color, odor, clarity, floating, settled and suspended solids, foam and oil sheen. Use those observations alongside your lab data.
For the paired approach, take total and dissolved samples at the same time. Filter the dissolved sample promptly, in the field or lab as your analytical method requires, and confirm the procedure with your laboratory before the storm. Record pH and hardness at the same moment. Sample more than once, because a single storm can mislead you.
Which housekeeping and source-control practices reduce lead before treatment?
Sweep metal fines, cover scrap and stock, and keep work areas out of the drainage path. Vacuum sweeping picks up fines before rain turns them into dissolved ions. Roofing or tarping stored material limits contact with rain. Moving grinding, cutting and cleaning operations under cover or onto contained pads keeps debris away from catch basins. Keep inlet protection and sediment traps maintained so particulate lead does not pass through. These steps lower your load and often shrink the treatment you need.
Which treatment technologies remove dissolved lead?
Sediment controls will not remove dissolved lead, because they target particles. For the dissolved fraction, we make Smart Sponge® HM media, which targets dissolved metals including lead, zinc, copper, arsenic and selenium, along with phosphorus. Metals are held at the media surface. Results depend on the water being treated, including factors such as pH, hardness and organic carbon, so removal rates should not be assumed. If your site also has hydrocarbons or elevated organic carbon, different Smart Sponge® media can be combined in one system.
What format fits my site, and how do I test it?
Catch basin inserts suit sites where lead-bearing runoff concentrates at a few drains, while vessels, vaults or pumped skids suit larger or more variable flows. The Ultra Urban® Filter is custom-fabricated to a basin's geometry and retrofits existing basins without excavation, pumps or power. Bulk media can be loaded into vessels, skids, tanks or vaults you already have, and Smart Skid systems use pumps and flow controls.
Before full scale, we can run laboratory column testing on your own water sample. To start, schedule a site assessment so we can match media and format to your drainage and discharge targets.