North Dakota Proposed Benchmarks for Industrial Discharge

On January 15, the North Dakota Dept of Health released its proposed industrial stormwater discharge permit. One of the key requirements for North Dakota industrial dischargers is the requirement for stormwater monitoring and stormwater benchmarks. Selected industrial sectors require monitoring and need to meet benchmarks under the proposed permit, which is on public comment until February 15, 2010.

Wood and Paper Products
Applicability: Facilities with SIC code 2421-2426 (Sawing/Planning mills), 2491 (Wood
Preserving), 2493 (Reconstituted Wood Products), and 2631 (Paperboard Plants).

Benchmark Values

• pH 6.0 – 9.0 S.U.
• Total Suspended Solids 100 mg/L
• Chemical Oxygen Demand 120 mg/L
• Phenols, Total 1.0 mg/L
• Arsenic, Total 0.1685 mg/L
• Copper, Total(1) 0.0636 mg/L


Chemical and Related Products
Applicability: Facilities with SIC code 281 (Industrial Inorganic Chemicals), 282 (Plastics and Synthetic Materials), 284 (Soaps and Detergents) and 287 (Agricultural Chemicals).

Benchmark Values

• pH 6.0 – 9.0 S.U.
• Total Suspended Solids 100 mg/L
• Total Phosphorus 2.0 mg/L
• Ammonia (2) as N 15.0 mg/L
• Nitrates as Nitrogen 0.68 mg/l
• Chemical Oxygen Demand 120 mg/L
• Zinc, Total(1) 0.117 mg/L


Food and Related Products
Applicability: Facilities with SIC code 2011 (Meat Packing Plants), 2015 (Poultry Slaughtering and Processing), and 207 (Fats and Oils).

Benchmark Values

• Oil and Grease No visible sheen (15 mg/L)
• pH 6.0 – 9.0 S.U.
• Total Suspended Solids 100 mg/L
• Ammonia (2) as N 15.0 mg/L
• Nitrates as Nitrogen 0.68 mg/l
• 5-Day BOD 30 mg/L
• Chemical Oxygen Demand 120 mg/L
• Fecal Coliform 200 colonies/100mL


Primary Metal Industries
Applicability: Any facility classified as SIC code 33.

Benchmark Values

• pH 6.0 – 9.0 S.U.
• Total Suspended Solids 100 mg/L
• Lead, Total(1) 0.0816 mg/L
• Cadmium, Total(1) 0.0159 mg/L
• Arsenic, Total(1) 0.1685 mg/L
• Copper, Total(1) 0.0636 mg/L
• Zinc, Total(1) 0.117 mg/L


Hazardous Waste Treatment, Storage and Disposal
Applicability: Facilities that treat, store or dispose of hazardous wastes.

Benchmark Values

• pH 6.0 – 9.0 S.U.
• Chemical Oxygen Demand 120 mg/L
• Ammonia (2) as N 15 mg/L
• Arsenic, Total(1) 0.1685 mg/L
• Cadmium, Total(1) 0.0159 mg/L
• Lead, Total(1) 0.0816 mg/L
• Silver, Total(1) 0.0318 mg/L
• Cyanide, Total(1) 0.0636 mg/L
• Mercury, Total(1) 0.0024 mg/L
• Selenium, Total(1) 0.2385 mg/L


Landfills and Land Application
Applicability: Facilities associated with waste disposal at landfills, land application sites and open dumps that receive industrial waste.

Benchmark Values

• pH 6.0 – 9.0 S.U.
• Total Suspended Solid 100 mg/L
• Chemical Oxygen Demand 120 mg/L
• Lead, Total(1) 0.0816 mg/L
• Oil and Grease No visible sheen (15 mg/L)

Automobile Salvage Yards
Applicability: Facilities engaged in dismantling or wrecking used motor vehicles for parts recycling/resale and for scrap; SIC code 5015.

Benchmark Values

• Oil and Grease No visible sheen (15 mg/L)
• pH 6.0 – 9.0 S.U.
• Total Suspended Solids 100 mg/L
• Chemical Oxygen Demand 120 mg/L
• Lead, Total(1) 0.0816 mg/L

Scrap Recycling Facilities
Applicability: Facility engaged in processing, reclaiming and distribution of metal scrap and other waste materials; SIC code 5093.

Benchmark Values

• Oil and Grease No visible sheen (15 mg/L)
• pH 6.0 – 9.0 S.U.
• Total Suspended Solids 100 mg/L
• Chemical Oxygen Demand 120 mg/L
• Copper, Total(1) 0.0636 mg/L
• Lead, Total(1) 0.0816 mg/L
• Zinc, Total(1) 0.117 mg/L


Air Transportation
Applicability: Regional and Primary commercial Airports and Air Force Bases

Benchmark Values

• pH 6.0 – 9.0 S.U.
• Ammonia(2) as N 15.0 mg/L
• Nitrates as Nitrogen 0.68 mg/l
• 5-Day BOD 30 mg/L
• Chemical Oxygen Demand 120 mg/L


Notes:
1 Hardness dependent; values given are based on a water hardness of 100 mg/L as CaCO3.
2 Ammonia is pH dependent; value given is based on a pH of 8.0 s.u.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

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Revised Washington Benchmarks for Industrial Stormwater Discharge

Effective January 1, 20010, the Washington Department of Ecology has issued new benchmark concentrations for industrial stormwater discharges. Dischargers subject to the revised State industrial stormwater discharge permit must collect samples of stormwater discharge at least quarterly. Different levels of Corrective Action are required if dischargers exceed any of their respective benchmarks over one or more quarters.

The revised benchmarks are:

All Facilities:
Parameter Benchmark Value
Turbidity 25 NTU
pH Between 5.0 and 9.0
Oil Visible Sheen (Yes/No)
Total Copper Western WA: 14 ug/L, Eastern WA: 32 ug/L
Total Zinc 117 ug/L

Industrial Sector Specific Benchmarks:
Chemical and Allied Products ( SIC 28), Food and Kindred Products (SIC 20)
BOD5 30 mg/L
Nitrate/Nitrite 0.68 mg/L
Phosphorus 2.0 mg/L

Primary Metals (SIC 33), Metals Mining (SIC 10), Automobile Salvage and Scrap Recycling (5015 and 5093), Metals Fabricating (SIC 34)
Total Lead 81.6 ug/L
Total Petroleum Hydrocarbons 10 mg/L

Hazardous Waste Treatment, Storage and Disposal Facilities and Dangerous Waste Recyclers
COD 120 mg/L
Ammonia 2.1 mg/L
TSS 100 mg/L
Total Arsenic 150 ug/L
Total Cadmium 2.1 ug/L
Total Cyanide 22 ug/L
Total Lead 81.6 ug/L
Total Magnesium 64 ug/L
Total Mercury 1.4 ug/L
Total Selenium 5.0 ug/L
Total Silver 3.8 ug/L
Total Petroleum Hydrocarbons 10 mg/L

Air Transportation (SIC 45)
Ammonia 2.1 mg/L
BOD5 30 mg/L
COD 120 mg/L
Nitrate/Nitrite 0.68 mg/L

Timber Product Industry (SIC 24), Paper and Allied Products (SIC 26)
COD 120 mg/L
TSS 100 mg/L

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

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EPA OW - OPP Pesticide Assessment Methods Meetings

EPA Office of Water (OW) and Office of Pesticide Programs(OPP) have identified a need to harmonize methods used by the Offices to determine whether pesticides represent a concern for aquatic life. To address these concerns, the Agency has begun a process to explore how to build on the high quality science in both OW and OPP to develop additional tools and approaches to support a consistent and common set of effects characterization methods using best available information.

A number of regional public meetings are being planned between January 11 and 22, 2010 to solicit input on the Agency's initial thinking regarding methods, tools, and approaches that are being developed and evaluated by OPP and OW to assure that pesticide ecological effects are characterized consistently. The areas for consideration under this effort include:

• Development and evaluation of predictive tools for use in development of community level benchmarks;
• Development of aquatic life community level benchmarks with datasets that do not conform to the "1985 Guidelines'' used to derive water quality criteria;
• Derivation of aquatic life screening values for aquatic plants
  

In selecting and/or developing appropriate methodogies, EPA OW and OPP expects to consider the following criteria:

• Continue to be based upon sound science and utilize the available data,
• Be legally defensible under their respective statutory mandates,
• Be based upon methodologies that are as consistent and practical as possible,
• Be implementable at the Federal and State level.
• Be developed as quickly and efficiently as possible, and
• Reflect stakeholder input and comments.

During these meetings, EPA will also solicit input from Regional stakeholders regarding 1)additional sources of pesticide data and relevant reports, 2)white paper topics, 3) availability of data, tools, approaches, and data sets on aquatic toxicity that may be useful for this effort, 4)types of values that are used by states and/or regions for protecting aquatic life in the absence of ambient water quality criteria, and 5) examples of situations in which differences between OW and OPP assessment approaches were an issue.

Following these meetings, the Agency plans to develop a set of white papers, describing potential new tools and analytical approaches that may be used by the Agency, state pesticide and water quality agencies, and other stakeholders.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

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Arkansas ADEQ Proposed Stormwater Permit Benchmarks

Note: This article has been updated:

Final Arkansas ADEQ Industrial Storm Water Permit

**********************************************************

The Arkansas Department of Environmental Quality (ADEQ) has proposed a revised industrial stormwater permit. The permit is open for public comment until May 11, 2009.

The proposed permit includes stormwater quality benchmarks which apply to all permitted facilities, and additional benchmarks that apply to specific industrial sectors (see below).
[Read more about stormwater benchmarks]
[Read more about how benchmarks compare to typical stormwater discharge quality]

Benchmarks being proposed were derived from a wide range of sources, including:

EPA Ambient Water Quality Criteria - Acute Values
EPA Ambient Water Quality Criteria - Chronic Values
EPA Ambient Water Quality Criteria - Lowest Observed Effect Levels (LOEL) Acute Values
EPA Ambient Water Quality Criteria - Human Health Criteria for Consumption of Water and Organisms.
North Carolina State Benchmark Values
Colorado State Water Quality Standards
National Urban Runoff Program (NURP) median concentration
Median concentration of Stormwater Effluent Limitation Guideline (40 CFR Part 419)
Laboratory derived Minimum Level (ML) and Method Detection Level (MDL).


The benchmarks being proposed under the ADEQ NPDES permit are:

All permitted facilities:

pH 6.0 - 9.0 s.u.
Chemical Oxygen Demand (COD) 120
Total Suspended Solids (TSS) 100
Oil & Grease 15

In addition to the above benchmarks, the following effluent characteristics must also be monitored for individual industrial sectors.

SECTOR A: TIMBER PRODUCTS
General Sawmills and Planing Mills (SIC 2421)
Total Zinc 0.6840 mg/L

Wood Preserving (SIC 2491)
Total Arsenic 0.16854 mg/L
Total Copper 0.0756 mg/L

SECTOR C: CHEMICALS AND ALLIED PRODUCTS
Agricultural Chemicals (SIC 2873-2879)
Nitrate plus Nitrite Nitrogen 0.68 mg/L
Phosphorus 2.0 mg/L
Total Lead 0.5188 mg/L
Total Iron 1.0 mg/L
Total Zinc 0.6840 mg/L

Industrial Inorganic Chemicals (SIC 2812-2819)
Total Aluminum 0.75 mg/L
Total Iron 1.0 mg/L
Nitrate plus Nitrite Nitrogen 0.68 mg/L

Soaps, Detergents, Cosmetics, and Perfumes (SIC 2841-2844)
Total Zinc 0.6840 mg/L
Nitrate plus Nitrite Nitrogen 0.68 mg/L

Plastics, Synthetics, and Resins (SIC 2821-2824)
Total Zinc 0.6840 mg/L

SECTOR E: GLASS, CLAY, CEMENT, CONCRETE, AND GYPSUM PRODUCTS
Clay Product Manufacturers (SIC 3251- 3259, 3261-3269)
Total Aluminum 0.75 mg/L

Concrete and Gypsum Product Manufacturers (SIC 3271-3275)
Total Iron 1.0 mg/L

SECTOR F: PRIMARY METALS
Steel Works, Blast Furnaces, and Rolling and Finishing Mills (SIC 3312-3317)
Total Zinc 0.6840 mg/L
Total Aluminum 0.75 mg/L

Iron and Steel Foundries (SIC 3321-3325)
Total Zinc 0.6840 mg/L
Total Aluminum 0.75 mg/L
Total Copper 0.0756 mg/L
Total Iron 1.0 mg/L

Rolling, Drawing, and Extruding of Nonferrous Metals (SIC 3351-3357)
Total Zinc 0.6840 mg/L
Total Copper 0.0756 mg/L

Nonferrous Foundries (SIC 3363-3369)
Total Zinc 0.6840 mg/L
Total Copper 0.0756 mg/L

SECTOR G: METAL MINING (ORE MINING AND DRESSING)
Active Copper Ore Mining and Dressing Facilities (SIC 1021)
Nitrate plus Nitrite Nitrogen 0.68 mg/L

Iron Ores; Copper Ores; Lead and Zinc Ores; Gold and Silver Ores; Ferroalloy Ores, Except Vanadium; and Miscellaneous Metal Ores (SIC Codes 1011, 1021, 1031, 1041, 1044, 1061,
1081, 1094, 1099)
Total Antimony 0.636 mg/L
Total Arsenic 0.16854 mg/ L
Total Beryllium 0.13 mg/L
Total Cadmium 0.0118 mg/L
Total Copper 0.0756 mg/L
Total Iron 1.0 mg/L
Total Lead 0.5188 mg/L
Total Mercury 0.0024 mg/L
Total Nickel 6.43 mg/L
Total Selenium 0.2385 mg/L
Total Silver 0.0107 mg/L
Total Zinc 0.6840 mg/L

SECTOR H: COAL MINES AND COAL MINING-RELATED FACILITIES
Coal Mines and Related Areas (SIC 1221-1241)
Total Aluminum 0.75 mg/L
Total Iron 1.0 mg/L

SECTOR J: MINERAL MINING AND DRESSING
Sand and Gravel Mining (SIC 1442, 1446)
Nitrate plus Nitrite Nitrogen 0.68 mg/L

SECTOR K: HAZARDOUS WASTE TREATMENT, STORAGE, OR DISPOSAL FACILITIES
Ammonia 19 mg/L
Total Magnesium 0.0636 mg/L
Total Arsenic 0.15 mg/L
Total Cadmium 0.0118 mg/L
Total Cyanide 0.0636 mg/ L
Total Lead 0.5188 mg/L
Total Mercury 0.0024 mg/ L
Total Selenium 0.2385 mg/L
Total Silver 0.0107 mg/L

SECTOR L: LANDFILLS, LAND APPLICATION SITES, AND OPEN DUMPS
Total Iron 1.0 mg/L

SECTOR M: AUTOMOBILE SALVAGE YARDS
Automobile Salvage Yards (SIC 5015)
Total Aluminum 0.75 mg/L
Total Iron 1.0 mg/L
Total Lead 0.5188 mg/L

SECTOR N: SCRAP RECYCLING FACILITIES
Scrap Recycling and Waste Recycling Facilities (SIC 5093)
Total Aluminum 0.75 mg/L
Total Copper 0.0756 mg/L
Total Iron 1.0 mg/L
Total Lead 0.5188 mg/L
Total Zinc 0.6840 mg/L

SECTOR O: STEAM ELECTRIC GENERATING FACILITIES
Total Iron 1.0 mg/L

SECTOR Q: WATER TRANSPORTATION
Water Transportation Facilities (SIC 4412-4499)
Total Aluminum 0.75 mg/L
Total Iron 1.0 mg/L
Total Lead 0.5188 mg/L
Total Zinc 0.6840 mg/L

SECTOR S: AIR TRANSPORTATION FACILITIES
Airports (SIC 4512-4581).
Ammonia 19 mg/L

SECTOR U: FOOD AND KINDRED PRODUCTS
Fats and Oils Products (SIC 2074-2079)
Nitrate plus Nitrite Nitrogen 0.68 mg/L

SECTOR Y: RUBBER, MISCELLANEOUS PLASTIC PRODUCTS, AND MISCELLANEOUS MANUFACTURING INDUSTRIES
Rubber Products Manufacturing (SIC 3011, 3021, 3052, 3053, 3061, 3069)
Total Zinc 0.6840 mg/L


SECTOR AA: FABRICATED METAL PRODUCTS
Fabricated Metal Products, except Coating (SIC 3411-3499; 3911-3915)
Total Aluminum 0.75 mg/L
Total Iron 1.0 mg/L
Total Zinc 0.6840 mg/L
Nitrate plus Nitrite Nitrogen 0.68 mg/L

Fabricated Metal Coating and Engraving (SIC 3479)
Nitrate plus Nitrite Nitrogen 0.68 mg/L
Total Zinc 0.6840 mg/L

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, stormwater and wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

Caltha LLP Aquatic Toxicology / WQ Standards Services Website

CT Stormwater Benchmarks for Copper, Lead, Zinc and Other

The Connecticut Department of Environmental Protection (“DEP”) has proposed to revise and renew its General Permit for the Discharge of Stormwater Associated with Industrial Activity. The previous General Permit was adopted in 2002, modified in 2003, and expired on March 31, 2008.

Recent proposals by DEP have significantly lowered numeric "benchmarks" associated with industrial stormwater discharges.

The 2002 permit required annual monitoring of stormwater discharges from qualifying storm events for an expansive list of chemical and physical parameters, including whole effluent toxicity, and a set of Target Values for the parameters based on the 80th percentile of the monitoring data collected in previous years.

In 2008, DEP announced that it would be revising the permit. It proposed to update its 80th percentile Target Values to reflect the monitoring data acquired since the prior permit was adopted in 2002. DER also proposed Action Levels at the 95th percentile of prior monitoring results which would require follow-up action by registrants to investigate the source of the exceedances and modify their BMPs and SWPPP.

On February 4, 2009, DEP issued a new proposed draft which adopts ten sectors modeled on the EPA “MSGP-2008” Multisector permit, with semi-annual monitoring. The previously proposed “Action Levels” have become “Benchmarks” to track the federal language. DEP’s proposal retains the broad spectrum of parameters to be included in the monitoring program, including toxicity, but makes some sector specific adjustments. The toxicity monitoring requirement carries with it no Benchmark. The draft also adds annual monitoring for parameters for which receiving waters have been designated impaired or subject to Total Maximum Daily Load restrictions.

The Benchmark values for copper, lead and zinc are based on Connecticut’s State Water Quality Standards. The Benchmarks for remaining parameters (pH, O&G, COD, TSS, TP, TKN, and NO3), are based on the 50th percentile of the previously acquired monitoring data.

DEP expects to go to notice on a new proposal in April 2009. In the meantime, the DEP has published notice that it intends to extend the 2002 General Permit once again until September 30, 2010.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

Caltha LLP Aquatic Toxicology / WQ Standards Services Website

Use of Aquatic Life Standards As Stormwater Benchmark Values

On July 6, 2009, the Minnesota Pollution Control Agency (MPCA) released the draft of its proposed multi-sector industrial stormwater discharge general permit. This permit, once promulgated, will replace the existing industrial stormwater permit, which expired in October of 2002.

The MPCA draft permit is of interest outside of Minnesota because of the numerous unique requirements that MPCA has included. Many of these go well beyond other current State general permits, and even the most recent US EPA general permit (“MSGP-2008”). Unique features of the MPCA permit include special stormwater antidegradation requirements, design and performance requirements for stormwater infiltration, requirements for mercury minimization, and others.

One unique feature of the draft MPCA general permit is the use of Aquatic Life Standards as Stormwater Benchmarks. Stormwater benchmarks are used to evaluate the effectiveness of stormwater Best Management Practices (BMP). MPCA is currently proposing to use some Final Acute Values (FAV) and “Great Lakes” derived water quality standards as stormwater benchmarks. For other proposed benchmarks, “Best Professional Judgment” is the basis for the values.

MPCA is proposing to use FAV that apply to cold water fisheries or “trout streams” (Class 2A) for a number of benchmark chemicals, including:

Aluminum
Ammonia
Arsenic
Cadmium
Chromium
Copper
Cyanide
Lead
Nitrogen
Phenol
Selenium
Silver
Zinc

For some of these chemicals, MPCA is apparently considering water quality-based adjustments, based on parameters such as hardness, pH, temperature, etc.

These water quality-based benchmarks, as proposed, would not apply to all industrial categories. The industry sectors that would be subject to one or more water quality derived benchmarks include:

Sector A - Timber Products
Sector C - Chemical and Allied Products Manufacturing
Sector E - Glass, Clay, Cement, Concrete, and Gypsum Products
Sector I - Oil and Gas Extraction and Refining
Sector K - Hazardous Waste Treatment, Storage, or Disposal Facilities
Sector L - Landfills, Land Application Sites, and Open Dumps
Sector M - Automobile Salvage Yards
Sector N - Scrap Recycling and Waste Recycling Facilities
Sector Q - Water Transportation
Sector U - Food and Kindred Products
Sector X - Printing and Publishing
Sector Y - Rubber, Miscellaneous Plastic Products, and Miscellaneous Manufacturing
Industries
Sector Z - Leather Tanning and Finishing
Sector AA - Fabricated Metal Products
Sector AC - Electronic and Electrical Equipment and Components

Looking for other sector information? Click here for information on proposed stormwater requirements for a specific sector.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

Caltha LLP Aquatic Toxicology / WQ Standards Services Website

EPA Pesticide Aquatic Life Benchmarks - Water Quality Criteria Comparison

Two Offices within US EPA derive “standards” for pesticides to protect aquatic life. However, the methods used to derive these “standards” are quite different, as are the intended uses for the information.

Aquatic life benchmarks are derived by Office of Pesticide Programs (OPP) to assist in performing its responsibilities to regulate pesticides used in the US. OPP aquatic life benchmarks are determined based on toxicity data reviewed by the Agency during its most recent risk assessment as part of the pesticide registration process. OPP relies on studies required under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) as well as laboratory and field studies available in the public scientific literature to assess environmental risk. Aquatic life benchmarks represent the most sensitive toxicity endpoint for a given aquatic organism using all scientifically acceptable toxicity data available to EPA. OPP then uses these aquatic benchmarks in risk assessments developed for pesticides. The benchmarks can be helpful in interpreting monitoring data, and to identify and prioritize sites and pesticides that may require further investigation.

[Read more about other types of "benchmarks" used by EPA and States in NPDES permits]

The US EPA Office of Water (OW) has the responsibility for evaluating aquatic toxicity data to assess the ecological effects of chemicals in surface water. The OW uses aquatic toxicity data to develop national ambient water quality criteria that can then be adopted by States and tribes to establish water quality standards under the Clean Water Act (CWA). These standards are used to determine if individual water bodies meet their intended uses, and in setting NPDES permit discharge limits. Ambient Water Quality Criteria are derived for a wide range of chemicals, which include certain chemicals which are registered by OPP under FIFRA.

In contrast to OPP benchmarks, ambient water quality criteria derived by OW are based on a statistical evaluation of the available toxicity data. This approach derives a concentration to protect the integrity of the aquatic community rather than selecting a concentration that is protective of the single most sensitive organism.

OPP and OW are currently working together to harmonize the scientific approaches that now underlie both programs. A harmonized approach is expected to result in consistent tools and approaches to use in ensuring the protection of aquatic ecosystems.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

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Stormwater Benchmark Values - Benchmarks for TSS

About one-third of US States include chemical monitoring in their general stormwater discharges permits. Over time, this percentage has been increasing as States revise their permits as they expire.

[Read about recent trends in industrial stormwater permit requirements across US]

For States that require chemical analysis of stormwater samples, “benchmark” concentrations or values are often included. Benchmark concentrations can be specified for a number of different chemical parameters, but the more common chemicals which are assigned benchmarks include total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), nutrients and heavy metals.

Benchmark values differ from permit limits. In a typical wastewater NPDES permit, limits may be specified for chemical parameters; if any of the limits are exceeded, it becomes a violation of the permit and may be subject to enforcement action.

Benchmark values are intended to provide a measurement of the effectiveness of the stormwater pollution prevention plan (SWPPP). Exceeding a benchmark does not directly result in a permit violation. However, permits typically require facilities to reevaluate their SWPPP and to take prompt corrective action after a benchmark value is exceeded. Failure to take prompt corrective action if a benchmark value is exceeded can be a permit violation and subject to enforcement action.

Benchmark values tend to be fairly stringent. For example, a common benchmark concentration for total suspended solids (TSS) is 100 mg/L. To put this concentration into perspective, it is roughly equivalent to 1 teaspoon of sediment added to 14.5 gallons of water.

As a sector example, US EPA tested the stormwater discharge at 185 transportation and warehousing facilities. The average TSS was reported as 466 mg/L and half the facilities sampled exceeded 159 mg/L (Federal Register Vol. 60, No. 189). Based on these data, over one-half of transportation and warehouse sites would not meet the 100 mg/L benchmark.

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

For more information on Stormwater Permitting & Compliance Services, go to:
Caltha LLP SWPPP - Stormwater Services Website

Turbidity Effluent Limits for Stormwater Discharges

In December 2008, US EPA published proposed effluent limits for stormwater discharges from construction sites. The proposed rules included a numeric effluent limit of 90 NTU. NTUs are a standard measurement of turbidity in water and of suspended material in the water.

[Read more about proposed stormwater effluent standards]

Benchmark values and previous stormwater effluent limits have always been expressed as Total Suspended Solids (TSS). Turbidity is related to TSS, however the relationship between turbidity and TSS is not always direct, and will be affected by a number of different factors.

Stormwater benchmark concentrations for TSS usually range from 100 to 250 mg/L. Using a few typical conversions between NTU and TSS, it is predicted that an effluent limit of 90 NTU will be roughly equivalent to 45 to 65 mg/L expressed as TSS. Therefore, it is projected that the proposed stormwater effluent limit is about one-half the lowest current benchmark concentration for TSS.

[Read more about the use of stormwater benchmark values]

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

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NPDES Permit Benchmark Value vs Permit Limitation

How are "benchmark values" in my NPDES permit different than my permit limits"?

Benchmark values differ from permit limits. In a typical wastewater NPDES permit, limits may be specified for chemical parameters; if any of the limits are exceeded, it becomes a violation of the permit and may be subject to enforcement action.

Benchmark values, in the context of stormwater NPDES permits, are intended to provide a measurement of the effectiveness of the stormwater pollution prevention plan (SWPPP). Exceeding a benchmark does not directly result in a permit violation. However, permits typically require facilities to reevaluate their SWPPP and to take prompt corrective action after a benchmark value is exceeded. Failure to take prompt corrective action if a benchmark value is exceeded can be a permit violation and subject to enforcement action. Multiple exceedances of a benchmark could result in a State requiring that the facility apply for an individual stormwater discharge permit. In this case, legally enforceable stormwater discharge limits may be written into the permit.

[read more about selecting appropriate stormwater monitoring techniques]

Caltha LLP provides expert consulting services to public and private sector clients nationwide to address water quality standards, wastewater permitting and assessing potential impacts of chemicals in the aquatic environment.

Caltha LLP Aquatic Toxicology / WQ Standards Services Website