Arizona DEQ Stormwater Monitoring and Industrial Storm Water Benchmarks

In December 2010, the Arizona Department of Environmental Quality (ADEQ) issued the Multi-Sector General Permit (MSGP) for industrial stormwater discharges. The revised permit included significant changes to stormwater discharge requirements for permitted sites, which are now divided into 29 industrial sectors. One of the most significant changes was the requirement for sampling stormwater and reporting results to ADEQ. The monitoring requirement begins immediately after permit coverage begins. ADEQ has defined monitoring seasons in the permit:
Summer wet season: June 1 – October 31
Winter wet season: November 1 – May 31
The frequency for stormwater sampling in the permit is at least twice each wet season (summer and winter) from each monitoring location.

All sites permitted under the MSGP (with some limited exceptions) will have to collect stormwater samples and have samples analyzed for their sector-specific benchmark parameters. If one or more benchmarks are exceeded, sites will be required to upgrade their pollution prevention measures and will need to do further stormwater monitoring.

Some stormwater benchmarks that apply to several sectors include:

Ammonia 2.14 mg/L
Biochemical Oxygen Demand (BOD) 30 mg/L
Chemical Oxygen Demand (COD) 120 mg/L
pH 6.0 – 9.0 s.u.
Total Aluminum 0.75 mg/ L
Total Arsenic 0.15 mg/L
Total Cyanide 0.022 mg/ L
Total Iron 1.0 mg/L
Total Magnesium 0.064 mg/L
Total Mercury 0.0014 mg/L
Total Selenium 0.005 mg/L
Total Suspended Solids (TSS) 100 mg/L


Since the 1980s, the U.S. Environmental Protection Agency (EPA) has collected industry-sector data on stormwater discharge. The linked presentation provides a comparison of these historic industrial stormwater results to the many of the ADEQ stormwater benchmark concentrations. The results are discussed in context of which stormwater benchmark parameters have a higher potential for exceedance of benchmark values. This presentation also discusses which of the industrial sectors have a higher potential for exceedance of their specific benchmark values.

Note: Arizona uses the same benchmark concentrations used by EPA and many other States; although the this linked presentation was specific to Minnesota, the analysis and conclusions apply to Arizona.
Link to presentation slides:

Industrial Stormwater Benchmarks – Comparison of New Minnesota Benchmark Concentrations To Historic Industry-specific Testing Results
Caltha LLP provides expert consulting services to public and private sector clients in Arizona to address Stormwater Permitting & Regulatory Support, Stormwater Pollution Prevention Plans (SWPPP), Stormwater Monitoring and Stormwater Training.


For further information contact Caltha LLP at
info@calthacompany.com or Caltha LLP Website