The Importance of SWPPPs for Former Dairy Sites

Oct. 1, 2009

California has been home to a majority of the dairies in the United States. Recently, a shift in land use has occurred through the state from agriculture to urban development. The Chino Valley has long been an area specializing in orchard and row crops and, until recently, was the number one dairy area in the United States. Dairy farmers are making a transition to either retirement or a new location outside of California. Now homes are being built on former dairies and surrounding existing dairies.

New homes being constructed on former dairy sites can be a challenge for water quality. Former dairy uses generate potential runoff issues during construction related to the disturbance of the soil during land development. Wastes generated from these dairies are typically left onsite for cleanup during the land development phase of construction. Wastes that are encountered include manure, wash water, and stormwater runoff from manured areas. These pollutants contain high levels of bacteria, biochemical oxygen demand, ammonia, nitrate, phosphorus, and other salts.

During construction activities, runoff from a project that is located on a former dairy site has the potential to discharge these pollutants to the storm drain system and ultimately to the receiving water system. Additionally, should the need for dewatering occur during the land development phase of construction, the existence of manure onsite can result in significant water pollution, specifically total dissolved solids (TDS) and nitrate.

During the operation of a dairy, water-quality issues are addressed through permits issued by the various regional boards. An Engineered waste management plan is required that provides a plan for managing manure and wastewater during the operation of a dairy. Typically, manure is collected from corrals and other areas several times a year and stored onsite. Twice a year, the manure is removed from the dairy and disposed of properly. Some manure is allowed to be utilized for crop production and remains on the property or within the watershed area. Ponds are built to manage the wastewater generated from the dairy operations. Ponds must be designed to retain the runoff from a 24-hour, 25-year storm event, and these ponds periodically must be cleaned out and the waste disposed of.

When a dairy is closed down, the site is left with soil laden with manure and other pollutants and ponds that may or may not still have water and/or waste left behind. Dairy structures may still exist that must be demolished prior to redevelopment. The developer will be responsible for the proper management and disposal of the contaminated wastes left behind. If the project is greater than 1 acre in size, then coverage under the Construction General Permit for Stormwater Discharges is required. A Notice of Intent must be completed and filed with the State Water Board, and a stormwater pollution prevention plan (SWPPP) must be prepared and implemented.

Planning is a critical component of a successful SWPPP program on any construction site. It is even more important on a former dairy site. The basis for the decisions made in preparing the SWPPP includes collecting information such as the site history, disturbed areas, contractor activities, and the potential for erosion. The need to properly address the pollutants of concern is the key to the successful implementation and ultimate completion of the SWPPP program and site development. Existing site characteristics and past land usages are critical components of the SWPPP.

Once this planning stage is complete, the preparation of the SWPPP begins. During the planning stage, a task that must be completed is the creating the pollutants of concern list. This list, in addition to the common materials and pollutants that you find on a construction site, will likely include wastewater from the ponds, stockpiled manure, and soil with high concentrations of manure, as well as the potential for high levels of TDS and nitrates. Determining whether or not your construction site drains to an impaired, or 303(d)-listed, water body is a part of the research that must be done prior to preparing the SWPPP.

Many receiving waters in areas where there are high concentrations of dairies have impairment due to the pollutants typically found on former dairy sites. If your site drains to a water body that is impaired for TDS or nitrates, for example, additional best management practices (BMPs) must be implemented to ensure that the water-quality standards for those constituents are not exceeded during construction activities. Most likely, sampling will be necessary to ensure that the water-quality standards are not exceeded throughout the land development phase of the project. But, regardless of the receiving water, dairy decommissioning requires BMPs to be implemented to prevent the potential for runoff of contaminated water or soil into the storm drain system.

With the pollutants of concern identified, the next step of SWPPP preparation is to identify the BMPs that will be used to address the various pollutants that you will come into contact with during the construction phase. Addressing stockpiles of manure, disposing of the manure, disposing of contaminated soil, and managing runoff that comes into contact with manure or contaminated soil are all issues that are essential to include in the SWPPP preparation.

First, look at your site. What are the drainage characteristics of the site now, and what will they be after the land development occurs? Where are the areas of concern? Have the locations of the manure stockpiles, the ponds, and other features been identified? What time of year are you going to be conducting the land development activities? Will you be grading in the winter? Is it a flat site, or is it sloped? Are there upstream activities that should be identified for potential runon? Are there downstream site issues? Is there a receiving water located close to the site? Can offsite drainage be diverted?

The selection of BMPs is typically broken down into a three-step process: Define the objective of the BMP; identify the BMP category; and select the appropriate BMPs. The selection and implementation of the BMPs should be based on the risks associated with the site itself. BMP objectives are pretty simple: control erosion and the discharge of sediment, and manage your non-stormwater discharges by managing the materials and activities on site during construction.

As is typical with any grading project, dirt is disturbed and the primary BMPs to be implemented are sediment control BMPs. However, there are several erosion control BMPs that can be used, alone or in combination, that prevent erosion by intercepting, diverting, conveying, and discharging flows in a manageable way. Using drainage swales, velocity dissipaters, and perhaps even slope drains can help keep stormwater from coming into contact with manure stockpiles or ponds.

Now that you have a feel for the site, know the drainage characteristics, and have selected appropriate erosion control BMPs that will control offsite drainage and other drainage issues on the site, it’s time to select the sediment control BMPs to be used. Of course, an appropriate perimeter control is necessary. While the perimeter control is your last line of defense and shouldn’t be relied on, it is an important BMP to include. Choosing the appropriate perimeter control BMP depends on soil type, climate, and local regulations. Silt fence can be a very effective sediment control BMP in most areas; however, high wind events can cause damage to even well-installed silt fence. Keeping the goal in mind–retain non-stormwater discharges (manure and manure-laden runoff) onsite–choose the BMP that best fits your site conditions and local regulations.

Keep the dirt on the site. Tracking control BMPs are an important component of the program to ensure that manure and soil contaminated with manure are not tracked out of the project site onto the streets. Installing a standard stabilized construction entrance may not be enough during the land development phase of development. A wheel-wash system may be necessary to control the migration of contaminated soil off the project location and into public streets and storm drain system.

During the first phases of the development, it is likely that there will be manure and contaminated soil that will need to be removed from the site. This is where good planning comes into play and is critical to ensuring that the contaminated materials are handled and disposed of in a proper manner. Wastewater ponds must be removed and the manure appropriately disposed of. Typically, upon decommission of a dairy, the structures are removed and disposed of as normal construction debris. However, when dealing with the manure and contaminated soil, the management and disposal is a little more complex. Ponds are typically cleared out and all the manure waste is stockpiled until ready for disposal. The wastewater from these ponds generally has high levels of salinity, nitrates, and other pollutants of concern. If there is wastewater remaining on your site prior to development that must be removed, it must be treated prior to discharge to the storm drain system to meet the water-quality standards of the region. Dairy wastewater can have a significant impact on both groundwater and surface water and must not be allowed to be discharged without first ensuring that the water-quality standards are being met. Usually, this means utilizing an active treatment system designed to address the specific pollutants of concern. Recently, UV radiation technology has been used to lower the levels of bacteria in the waste water.

Manure and manure-laden soil are typically shipped to a commercial fertilizer facility where the manure is transformed into fertilizer for sale to the public. Manure and soil from the ponds must be “cured” or stored for a period of time. It has been determined that it is most beneficial for manure to cure is 90 to 180 days prior to composting or crop application. Most commercial fertilizer facilities prefer to receive manure that is at least 150 days old. Providing 150 to 180 days of curing allows the moisture content to sufficiently reduce, making the manure and soil lighter per unit of volume and easier and less expensive to haul.

Manure stockpiles should be contained using a sediment control BMP such as fiber rolls. It may be necessary to provide dust control by covering the stockpiles until they are removed from the site. Going back to your first set of BMPs identified for this project, your diversion/interception BMPs, make sure that drainage on the site is diverted from the stockpile location. This will significantly lower your risk of stormwater coming into contact with the manure stockpiles and having a discharge of non-stormwater.

Scheduling is one of the most important and most overlooked BMPs available. Scheduling construction activities to occur in the summer can eliminate a larger portion of risk from your project. However, in California, even during the rainy season, there are plenty of dry days to conduct construction activities, so you must be prepared if you plan on working during the winter. If your project is going to be active during the rainy season, additional BMPs will be required to ensure that your site remains in compliance with the Construction General Permit as well as any local regulations. It is likely that if grading is going to occur during the rainy season, there will be a need for temporary sediment basins to be installed. Sediment basins are designed to capture and retain stormwater for a particular design storm. The SWPPP should include the design for any sediment basins that will be installed during the rainy season.

These basins should be installed prior to the beginning of the rainy season and be functional and ready to operate with the first rain event. Stormwater that comes into contact with any contaminated soil or manure stockpiles will need to be retained onsite in these sediment basins during rain events. If the manure stockpiles are covered and drainage is diverted away from those locations, then you have eliminated a risk of a non- stormwater discharge of water that has come into contact with a pollutant load that exceeds water-quality standards. You may need to sample and test the contained water prior to discharging it to a storm drain system to ensure that the water-quality standards are not exceeded. Treatment may be required to address the contained water as it will likely test positive for pathogens and other pollutants. Recent developments in UV technology have been effective in reducing the levels of pathogens in water and may be necessary in order to discharge the contained water.

And of course, maintenance is the key to proper BMP function. The SWPPP identifies an inspection schedule that will tell you when to conduct your BMP inspections. Most likely, you will be conducting inspections weekly and during storm events. Inspection reports should identify any BMP deficiencies and required corrective actions. Maintenance should be conducted on a routine schedule to ensure that the BMPs continue to function as designed. As the project progresses, there will likely be a need to move, add, and remove BMPs as the manure stockpiles continue to be disposed of.

Managing the manure and wastewater on former dairy sites will continue to be a critical issue for the Chino Basin, the Central Valley where the majority of dairies and former dairies are located, and other similar areas. With the technology available today and the variety of products on the market, a solution for any situation can be found.

About the Author

Jeanne Duarte

Jeanne Duarte, CPESC, CISEC, is president and cofounder of Storm Water Resources in Valencia, CA.

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