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Are Nutrient Offsets the Cost Effective Answer to Your
Stormwater Quality Compliance?

 

Developers and property owners are often on the hook for expensive BMPs or manufactured stormwater devices to meet increasingly stringent water quality standards. Nutrient Offsets have emerged as a new tool to control development costs associated with stormwater quality.

What are nutrient offsets?

Nutrient offsets are similar in concept to other types of environmental credits (i.e., wetland and stream banks), and are developed through the implementation of predominantly land-based nutrient-reducing activities such as land conversion (converting crop land to forest) and the use of agricultural BMPs. Based on the type and level of nutrient reduction activity, a resulting number of phosphorus and nitrogen offsets are generated. These credits can be purchased from a nutrient banker to meet your stormwater quality phosphorus removal requirements. Nutrient offset banks are reviewed and approved by DCR and DEQ.

Where can I use nutrient offsets?

In accordance with State law, nutrient offsets can be used in any watershed within the State that currently has a nutrient offset bank and where your project is not discharging to an impaired water body. These watersheds include the James River and the Rappahannock River. Nutrient banks are currently in the permitting or implementation stage for the Potomac River and the York River. Nutrient offsets can be used Statewide to meet the water quality requirements for VSMP permits and for local stormwater quality requirements including the Chesapeake Bay localities.

When can I use nutrient offsets?

Offsets may be used in meeting phosphorus-based stormwater quality requirements under the VSMP stormwater programs administered by DCR and localities when:

• The project area contains less than 5 acres of land disturbance; or
• The post-construction phosphorus removal requirement is less than 10 pounds per year; or
• You have demonstrated that you meet at least 75% of the phosphorus removal requirement for the project on-site; or
• You are replacing on-site water quality BMPs (e.g., in-ground manufactured devices or stormwater management ponds providing quality treatment) that are not functioning as designed.

Why would I want to use nutrient offsets?

The most important advantage nutrient offsets may provide is cost savings. Manufactured stormwater devices for providing water quality treatment typically cost in excess of $20,000 per pound of phosphorus removal. This does not even include the annual maintenance costs associated with these devices and the possibility of having to replace them at some point in time. Offsets are a one time transaction.

Offsets take up no real estate. A BMP designed to provide water quality treatment may be 25% to 50% larger that a BMP designed to provide quantity control only. The value of this additional real estate may more than make up for the cost of the offsets in additional land that can be used for development. Offsets offer a level of flexibility in site design, and are especially useful for redevelopment projects and other projects that face site constraints including limited area, grading issues, limited soil permeability or other design constraints.

Offsets may allow you to increase the site density. The ability to achieve the required water quality treatment levels can be a limiting factor to the amount of developed or impervious area that you can have on a site. Using offsets to assist you in reaching your water quality compliance to achieve that last 25%, you may gain more developed area on the site.

Want to learn about nutrient offsets or have your project evaluated for potential cost savings?

If you have additional questions regarding nutrient offset use or policy or would like to have your development project looked at to see if nutrient offsets are appropriate, please call Paul Hinson, P.E., LEED AP at 804-200-1914 or email him.