As cooler weather moves in, I hope you find time to kick back with a warm cup of your beverage of choice and this article considering Settling Time. For this article we will talk about different factors which impact how long it takes for particulates to settle out of stormwater once in the retention basin.

Stormwater retention basins are features that help to do the following:
*  Hold back water to help mitigate downstream flooding.
*  Settle out particulates to improve downstream water quality.
*  Slow down the rate of stormwater flow to help control erosion.
​*  Lower the temperature of the stormwater before it can flow downstream.​

As storm water flows over construction sites, parking lots and roads it picks up dirt and other debris that make up the suspended solids. The suspended solids can be sand, clay, silt and other particulates. The sediment load will vary based on the amount and duration of the rain event. Once the stormwater reaches the basin its flowrate drops off. In a quiescent pool the solids carried by the stormwater are given time to settle. If there is still flow through the pool or a second rain event occurs particulates may not have time to completely settle. These flow conditions would result in dynamic settling or possibly resuspension of sediment. Some particles are so small they will not settle. Others will have a settling time that is based on their particle size, shape, density and the water temperature. Solid settling in a stormwater basin can be estimated by Stokes’ Law.

Where:
V = settling velocity of the solid
g = acceleration of gravity (constant)
p1= mass density of the solid
p = mass density of water (constant)
d = diameter of the solid (assuming spherical shape)
µ= kinematic viscosity of water (varies only with temperature).

From the above equation we can see that particulates of higher mass density (p1) will settle out a bit more quickly than particles with lower mass density. (p1) We can also see that larger diameter (d2) particulates will settle out much faster than smaller particles. As diameter increases the settling velocity increases exponentially. Suspended solids vary in size with a particle of coarse sand being about 1,000x larger than a particle of fine clay. Given the larger diameter of the sand particles, we would expect them to settle much more rapidly than clay. Lastly temperature comes into play. Water becomes more viscous (µ) as temperature decreases. This higher viscosity leads to slower settling times.

Other factors come into play when considering settling time. Though the Stokes equation assumes that particles are round, few particles would be perfectly spherical. The irregular shaped particles would likely settle more slowly. Concentration of particles also plays a role. Like snowflakes falling from the sky, sediment particles can collide forming larger floc particles. These floc particles will settle more rapidly. In fact, flocculant is sometimes used to bond to suspended sediment or chemicals to sink them to the bottom and reduce the amount of polluted water leaving the basin. Chemical properties will also play a role. An extreme being road salt. The salt mineral is dense and of large diameter but will dissolve into the water. 

The dissolved road salt will not settle out of the stormwater. Particles with a greater attraction to water will settle out more slowly or will remain in solution.
A well designed and maintained basin will slow water and hold it long enough to allow sediment to drop out of solution. Oversizing a basin is one way to ensure plenty of settling time. Depth of the basin also comes into play by providing a large enough sediment storage zone. Maximizing the distance between the inflow and outflow helps maximize detention time. The challenge is designing a basin that will provide time for solids to settle, store sediment, minimize the valuable real estate it will take up and provide for easy maintenance down the road. 
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For more information contact our office at 513.695.1337

​You may have heard lately that Ohio is in a drought. A recently released drought map indicates Warren County to be in a severe to extreme drought. During these dry times, your construction site may welcome the lack of rain as dry sites can be easier to move around on and experience fewer issues with sediment and erosion control. However, we can’t get complacent on sediment and erosion control. The battle must go on!

In this month’s Development Digest, we will discuss remaining vigilant during dry times by having a routine dust control program in place, as well as making sure site BMPs are ready to go for the big rain. Dust can be a real problem during times of drought. So much so, that Soil and Water Conservation Districts were established to combat this issue, after the Great Dust Bowl of the 1930s. Poor farming practices, dry conditions, high winds, and plowing all combined to stir up the earth and create massive dust storms throughout the Midwest. President FDR signed the Soil Conservation Act of 1935 to protect our Country’s soil and water resources. This led to the establishment of the Ohio Soil and Water Conservation Commission (OSWCC) in 1941, which allowed funding to create Soil and Water Conservation Districts throughout the state. On construction sites, we often focus on keeping sediment contained during rain events, but soil loss can also occur during a drought. That’s why it’s important establish a dust control routine to keep sediment contained. Dust can be a real problem, as it is considered an airborne contaminant. Nearby existing homes and property can be covered in dust. It can become a public health concern when residents have trouble breathing. Our office has been receiving complaints from many sites throughout the county and we have been working with site contractors to ensure dust control measures are being enacted. 
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This can become a sleeping monster if dust control isn’t implemented. During times of extended drought, the ground becomes drier and harder. Especially in Warren County where much of the soil is clay, the ground can become like an impervious surface when it is compacted, dried and hardened. So, when it does eventually rain, the first initial downpour will likely run off the surface quickly, like it would on pavement. To further compound the issue, vehicles driving around on the site stirs up the sediment, creating dust clouds that will settle on the hard ground.  This fine-grained dust that settles accumulates almost like the regolith and dust on the surface of the moon. We are seeing anywhere from 1 to 3 inches of dust settled on some sites lately. 

4. Stone- Install crushed stone on graded roadways with construction traffic.
5. Barriers- Snow fencing or other suitable barriers may be placed perpendicular to wind currents to control air currents and blowing soil.
6. Calcium Chloride- the chemical may be applied by mechanical spreader as loose, dry granules. Follow manufacturer’s specs.
7. Operation and Maintenance- Repetitive, routine treatment of dust control practices.
8. Street Cleaning- Remove any settled dust from paved areas with a routine street sweeping schedule.

​Due to the recent drought, this is a great time to think about dust control. It looks like we will be getting some rain soon, so keep these practices in mind for the next dry time! If you have any questions regarding dust control you can contact us at the Warren County Soil and Water Conservation District website https://www.warrenswcd.com/ or by our phone number at (513) 695-1337.    

Additional Resources
 
Ohio EPA Rainwater and Land Development Manual. Chapter 7 Soil Stabilization – Dust Control: https://epa.ohio.gov/divisions-and-offices/surface-water/guides-manuals/rainwater-and-land-development?msclkid=cb5f60f4b48d11ec8b5ece1ef5e16d3c

In this month’s development digest, we will learn about storm drain tags, and how developers in Warren County can easily add them into their construction process to protect the natural waters. Storm drain tags are an important tool that we can use to keep pollutants out of the natural waters, and so this article will go into what a storm drain tag is, different types of tags, and why it is worth the extra little bit of effort to install these tags.
What is a storm drain tag?

• A storm drain tag is a type of label placed on a storm drain to prevent anyone from dumping harmful pollutants into the drain.
• The main purpose of the label is to provide a visual warning to keep people from illegally dumping into the drain, and to also provide education to those who may not know about the pollutants that can’t be dumped into the drain.

 
Why might a developer want to spend money on storm drain tags?

• Storm drain tags are an inexpensive way to promote a healthier and more environmentally conscious community.
• They can protect the integrity of storm drains.
• Ensuring that only rain goes down the drain will help keep retention basins clear and attractive. Reduces the need to use excess pond dye since the water is already healthy and clear.
• Can save money in the future by preventing spills of hazardous material that requires clean-up.

 
Types of Drain Tags

• There are a few main types of drain tags: Pre-cast, plastic, and metal tags.
  • Pre-cast: Pre-cast storm drain tags are casted onto the storm drain when the structure is built. Pre-cast tags require the least effort since they are made with the rest of the storm drain.
  • Plastic: Plastic storm drain tags are typically attached to the drain using glue. A substantial amount of glue should be used to install the tags to create a proper seal.
  • Metal: Metal storm drain tags can be installed either with glue like the plastic, or some tags have a bolt and a nut that holds the tag in the grate of the storm drain.
  • All three of these tags are effective methods to keep pollution from entering the drains.

 
If you have any questions regarding storm drain tags or the installation of the tags you can contact us at the Warren County Soil and Water Conservation District website https://www.warrenswcd.com/ or by our phone number at (513) 695-1337.
 
 
Additional Resources
Nonpoint Source Pollution – US EPA

​Sediment basins are designed to trap sediment from a construction site. If not maintained properly the basin can become filled with sediment and algae. While keeping sediment and algae out of the basin may seem like an impossible task, there are steps that can lessen the buildup and costly maintenance associated with dipping out or treating the basin. The following article covers sediment basin function, maintenance, and considerations to reduce algae.
Sediment Basin Basics
A sediment basin is a settling pond. By slowing down the flow of sediment-laden runoff, solids can settle out and sink to the bottom of the basin. The sediment basin is constructed as a first step, prior to land disturbing activities. The settling basin is usually converted to a wet retention basin or a dry detention basin at the end of the construction project. During construction, the basin functions for sediment control while after construction, the basin functions for stormwater flood control and water quality improvement practice.
How it Works 
As construction site runoff flows into the basin its flow rate is slowed on reaching the basin. Heavier sediment particles sink to the bottom while clean water remains in the top dewatering zone. As the water makes its way to the outlet a skimmer pulls water from near the surface and directs it through the principal spillway. During extreme rain events water would build up in the basin then flow through the riser and the principal spillway.

Maintenance for Proper Function and Control of Algae
For a basin to function, accumulated sediment must be removed from the sediment storage zone once it exceeds 50 percent of the minimum required sediment storage design capacity and prior to the conversion to the post-construction practice. Excess sediment in the basin decreases the depth of the dewatering zone, brings in other potential pollutants, such as nutrients. Sediment buildup also increases the maintenance required to keep the basin functional.  
The shallow water also allows additional sunlight to make its way to the bottom of the basin further warming the water. Shallow water promotes the growth of vegetation, algae, and mosquitos. Algae can increase maintenance needs by creating additional solids that settle to the basin bottom and fill the sediment storage zone with muck. Some blue green algae can also produce toxins making the water unsafe.
​
Prevent Early Fill-up of the Sediment Storage Zone
The following steps can help minimize maintenance needs while keeping the basin functional.

1. Stabilize the inner bank of the basin as early as possible utilizing grass seed and straw matting.
2. Remove sediment from inflow into the basin by utilizing stabilized grass swales, silt fence, or filter sock and other best management practices on the construction site.
3. Excavate the construction site in phases so that less of the dirt is exposed and subject to erosion.
4. Keep the disturbed area of the site as small as possible.
5. Stabilize the construction site as soon as possible.
6. Have a pond management company treat algae blooms before they become severe.
7. Dip sediment once it exceeds (50%) of the minimum required sediment storage and prior to conversion to post-construction.

Prevention of excess sediment in the basin is often more cost effective than bringing in heavy equipment to dip out the basin and then hauling off the sediment. These steps can also reduce resident and local homeowner association complaints down the road.
 
Additional information can be found in the Rainwater and Land Development Manual, Chapter 6

​Questions? Contact our office at 513.695.1337

​In an episode of Seinfeld, Newman is quoted as saying “The mail, it never stops Jerry!” The same can be said for maintenance of sediment & erosion control measures (SECMs) on construction sites; it is a never-ending battle, and it never stops!
 
Your project should have a stormwater team established to ensure that all SECMs are inspected once every 7 calendar days and after every > 0.5-inch rain event per 24-hour period by the end of the next calendar day (per Ohio EPA Construction General Permit requirements). The stormwater and resulting sediment-laden runoff, never stop. So that’s why it’s important that we remain vigilant and maintain the SECMs until the site is stabilized with grass.
 
Warren County SWCD conducts monthly site inspections to help your crew identify failing or missing BMPs to help you stay compliant with the Construction General Permit. When we encounter a project that has done a great job on installation and maintenance of the SECMs, we like to highlight it in our Development Digest for a job well done.
 
This month, we call attention to the Eastern Gas Transmission and Storage, Inc. (EGTS) Lebanon Compressor Station HP project in Clearcreek Township. EGTS boasts a robust environmental compliance division as well as an on-site stormwater team that has been great to work with. The stormwater team has followed the Stormwater Pollution Prevention Plan (SWPPP) to make sure the SECMs are properly installed and maintained.
 
Not only does the site exemplify superb examples of proper SECM installation, maintenance, and an inspection routine, but they also place an emphasis on employee safety. The focus on safety really demonstrates how it’s not just about protecting the environment, but also the people that work together to achieve a common goal.
 
The site is not without its challenges however, with a wetland conveniently nestled between construction areas. The stormwater team has highlighted the importance of protecting the wetland to prevent sediment from filling it in. Most of Ohio’s wetlands have been lost since the days when Ohio was a frontier state. EGTS understands the importance of protecting the ones we still have left. But don’t take my word for it! Hear it from the pros at EGTS:

​In closing, we at Warren County SWCD understand that development does not come without risks to the environment, that’s why it’s important that development happens in an environmentally conscious way. So, well done EGTS. May all other construction sites follow your lead!

​​Questions about BMPs?  Call Warren Co SWCD offices at (513) 695-1337

Fast moving water can cause a LOT of damage! Many problems can arise from water flowing at a high velocity. This is especially the case when talking about a high flow rate in concentrated areas such as ditches or swales. Erosion is an issue that can result from the high velocities that may occur in ditches or swales, and so it is important to find ways to mitigate the erosion in the best way possible. Check dams are a great option that can be installed in ditches and swales to decrease the water velocity and in some cases keep sediment from washing downstream.

​Check dams are constructed structures built up as a wall in a flow path that serves the purpose of slowing down water velocity. Many check dams consist of 4–8-inch stone and are no higher than 3 feet tall and are constructed along the width of the swale/ditch. Check dams can also be constructed of material such as compost filter sock. As mentioned above, check dams can also serve the purpose of keeping sediment from washing downstream. However, not all types of check dams are good for sediment control. Rock check dams are an effective way to slow down velocity and prevent erosion, however, rock is not an effective method to keep sediment from washing away due to the pore space in the material that sediment can wash right through. Filter socks are designed to keep sediment from washing downstream, and so if the goal is to slow the velocity of the water AND keep sediment in, then a filter sock check dam might be the best option.  

Maintenance Considerations:

• Per the Rainwater and Land Development manual, once sediment has built up to one-half the original height of the check dam, the sediment should be removed.
• Removal of the check dam should occur once earth disturbance has ended and the upland area has been stabilized. Once the check dam has been removed, the area should be graded and seeded to match the surrounding area per the design.
• Routine inspections are also a great way to ensure the check dam is working effectively.

 
For more information on the design criteria and specifications about check dams, please visit the OEPA Rainwater and Land Development Manual chapter 5.1. For regulations regarding construction and earth disturbance in Ohio please see the OEPA NPDES Construction General Permit.

BMP Blast: Silt Fence
 
What’s the first BMP that comes to mind when you think of construction site sediment control?  Chances are you thought of silt fence (SF)! This month, we dig into how this relatively inexpensive practice is used and some common installation pitfalls to avoid.
 
SF is a sediment-trapping barrier comprised of geotextile fabric and support posts. The fence is installed downslope of areas where sheet and rill erosion are expected to occur. Sediment-laden runoff ponds behind the fence and allows for deposition. Although it is a very popular and effective BMP, the Ohio Department of Natural Resources finds that about 75% of SF does not function due to poor installation. Here are some key points to follow:

• Follow the contour. Install SF on a level contour at least five feet away from the toe of a slope to promote sediment deposition. Each end of the SF should be “j-hooked” or curved slightly up the slope to prevent water from flowing around it. If the fence is installed up and down slopes, it will concentrate and channelize the runoff. Simply running a line of SF around the entire site may not be the most effective option. Consider installing discreet segments of silt fence along the topography as to not overwhelm the system.
• Trenching. Install SF with at least 8 inches of the geotextile fabric below ground. An un-trenched silt fence is useless because runoff will flow right under it.
• Pulled taut with strong posts. Install SF with the geotextile fabric pulled taut between strong wooden or metal posts spaced 5 to 10 feet apart. The posts should be located on the downslope side of the fence. Seams in the SF should occur at a post and overlap at least 6 inches. For a stronger fence, consider using wire backing.
• Backfill and compact. Fill the trench back in with dirt and compact it to secure the fence in place. Consider using a silt-fence installation machine which slices, installs, and backfills with ease.

Do not use SF…

• on steep slopes.
  
• as a check dam.
  
• below high velocity/high flow/concentrated flow areas.
  
• to capture drainage from areas larger than what is recommended.

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What kind of maintenance does silt fence require?

• Routine inspections after rainfall events
• Removal of sediment when it reaches one-half the height of the SF
• Replace damaged/torn fabric
• Repair downed SF

 
Assess what caused the failure and make changes to prevent it from happening again. Is there a concentrated flow pointing at the fence? Did someone drive over it? Is the fence sufficiently trenched and compacted? Is the drainage area too big?
 
For more details on the minimum criteria for SF fabric/posts and maximum slope length above SF, please refer to the Ohio Environmental Protection Agency’s (OEPA) Rainwater and Land Development Manual, Chapter 6.3.

In an effort to protect the health of our local waterways- rule 901:10-3-11 of the Ohio Administrative Code prohibits solid and liquid waste from being discharged into stormwater runoff. You know the drill- only rain should go down the drain!
 
Since the risk of stormwater pollution increases with construction activity and land development- the Ohio Environmental Protection Agency’s Construction General Permit (CGP) takes storm drain dumping prohibitions to another level. While the permit largely discusses sediment and erosion control measures, it also lists specific potential pollutants to be mindful of and requires a site-specific Stormwater Pollution Prevention Plan (SWPPP) be written and maintained.
 
Prohibited Discharges

• Concrete washout
• Stucco washout, paint, form release oils, curing compounds, and other construction materials
• Fuels, oils, and other vehicle fluids
• Soaps or solvents from vehicle and equipment washing
• Wastes from any activity that is expected to elevate concentrations of carcinogens, hydrocarbons, metals, or toxics in stormwater runoff

 
Other Potential Pollutants to Minimize

• Trash
• Sanitary wastes
• Landscape materials, fertilizers, pesticides, and herbicides

 
Spills and Unintended Releases
Intentionally dumping waste down the drain is certainly prohibited but accidental discharges are just as serious and should be addressed immediately. Keeping up on your periodic site inspections is a great way to identify and address these problems. When possible, locate dumpsters, fueling stations, concrete washout areas, and portable bathrooms away from storm drains and watercourses.
 
For more details on reportable quantities, please refer to this Release Reporting of a Hazardous Substance guide by the Ohio EPA. While an emergency can also constitute a violation, an emergency should be reported immediately to Ohio EPA’s 24-hour spill hotline at 1-800-282-9378 or 614-224-0946.
 
Additional Resources
Nearby Sanitary Landfills & Construction and Demolition Debris Facilities
Ohio EPA NPDES General Construction Permit (OHC000006)
Ohio Rainwater and Land Development Manual

In 1948, the Federal Water Pollution Control Act became the first U.S. law to combat water pollution. This act laid groundwork for the establishment of a cornerstone amendment- the Clean Water Act of 1972 (33 U.S.C. §1251 et seq 1972). This reorganization and expansion of the original act required every state to adopt water quality standards to protect, maintain, and improve the quality of the nation's surface waters.  The Clean Water Act requires a permit for any discharges from a point source into navigable waters. National Pollutant Discharge Elimination System (NPDES) Permits outline limits on the type and allowable amounts of certain constituents, monitoring requirements, and/or best management practices to mitigate water pollution. Limits and practices are put in place to protect water quality, aquatic life, and public health. The purpose of NPDES permitting is to help provide specific guidance for the overarching goals from the CWA.
 
Types of NPDES Permits:

• Individual 
• General 
• Pretreatment 
• Stormwater
• Biosolids 
• Concentrated Animal Feeding Operations

Municipal Separate Storm Sewer System (MS4) Stormwater NPDES Permit
 
An MS4 is owned by a state, city, town, village, or other public entity designed to collect or convey stormwater (e.g., storm drains, pipes, ditches) and discharge to waters of the U.S. These systems are not a combined sewer overflow system (like in Cincinnati, Columbus, Toledo, etc.), a part of a sewage treatment plant, nor a publicly owned treatment works (POTW). In contrast, stormwater runoff is transported through MS4s, and then discharged, untreated, into local water bodies. To prevent harmful pollutants from entering MS4s and natural waterways, these entities must obtain an NPDES permit and develop stormwater management programs (SWMPs).
 
The 1990 Phase I regulation requires medium and large cities or certain counties with populations of 100,000 or more to obtain NPDES permit coverage for their stormwater discharges. A local example of a Phase I community is Dayton, Ohio. The 1999 Phase II regulation requires small MS4s located fully or partially in urban areas with a population of at least 50,000 and MS4s designated by the permitting authority to obtain NPDES permit coverage for their stormwater discharges. Warren County and several contracted municipalities within the county (i.e., Mason, Deerfield, Lebanon) are regulated under Phase II of the permit.
 
Industrial Stormwater NPDES Permit
 
There are 11 categories of regulated industrial activities that include heavy, manufacturing, coal and mineral mining, hazardous waste treatment, metal scrap yards, transportation facilities, landfills, treatment works, and more. The complete list of facilities and activities subject to industrial stormwater regulations and additional information can be found here.

Oil and Gas Linear Transmission Stormwater
 
Certain oil and gas facilities and activities must have CWA section 402 permit coverage to discharge stormwater. Examples include improvements to public roads, conventional petro-refineries, ethanol plants, natural gas utility, commercially/privately owned hotels/RV parks/campgrounds, etc. More information and a more comprehensive list of non-exempt activities can be found here.
 
Ohio did not renew its Oil and Gas Linear Transmission Line permit (OHCG00001) which expired on September 16, 2023. Projects that obtained coverage under the now expired permit shall adhere to the conditions of the permit until the project is eligible to submit a Notice of Termination (NOT). Construction activities which cause a violation of Ohio’s water quality standards may lose exception from NPDES permitting.
 
NPDES Construction General Permit (GCP)
 
Construction activity is considered a point source discharge because specific locations where activity is happening can be identified. This contrasts with non-point source pollutants, which are wide-spread, diffuse sources of pollution across landscapes, so a single point cannot be easily identified. As previously mentioned, federal laws were put into place to prohibit point-source pollutants without an NPDES permit. An NPDES Construction General Permit (CGP) is required for any project that is going to be disturbing one acre or more of land or part of a common plan of development that will ultimately end up disturbing one acre or more. In Warren County, these projects also require an Earth Disturbing Permit (EDP). 

Earth Disturbing Permit in Warren County
 
In Warren County, prior to submitting the Notice of Intent (NOI) for the NPDES permit to the Ohio EPA, you must also apply for an EDP, which requires a complete Stormwater Pollution Prevention Plan (SWPPP) review and approval, submission of any necessary stormwater calculations, construction drawings, and the EDP application. This submission page and additional information for specific processes within different municipalities in the counties can be found here.
 
Our urban program specialists at Warren County SWCD are happy to answer any additional questions you may have regarding permit coverage requirement and the NPDES and EDP application process. You can give our office a call at 513-695-1337.
 
Additional Resources
 
US EPA NPDES Stormwater Program
US EPA NPDES Technical Resources
Earth Disturbing in Warren County
Ohio EPA MS4 Permit (OHQ000004)
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How does a concrete washout area promote workplace safety?
Concrete washout is a caustic and corrosive waste material with a pH of around 12. If an employee is exposed to washout, they can suffer serious skin irritation, chemical burns, and eye damage. Additionally, concrete washout contains toxic metals like Chromium, Nickel, Vanadium, and Zinc. Exposure in large amounts to these metals can cause long-term damage to the brain, lungs, kidneys, liver, and other important organs. Keeping waste contained to one or two designated areas will help minimize exposures and promote workplace safety.
​
What kind of maintenance does a concrete washout area require?

• Inspecting the area regularly to ensure no leaks occur
• Emptying the area of waste before it reaches capacity
• Cleaning up spilled or improperly disposed of slurry

 
Note: Washout waste is also created when using mortar, plaster, stucco, and grout and should also be disposed of properly.
 
Additional Resources
US EPA Concrete Washout Fact Sheet
OSHA Concrete Hazards
OEPA Rainwater and Land Development Manual
Ohio EPA NPDES General Construction Permit (OHC000006)