Anne Arundel County, Maryland

Anne Arundel County, Maryland

Our Expert:

LimnoTech helped Anne Arundel County update its stormwater Best Management Practice (BMP) database to ensure that it included the most complete, accurate, and up-to-date information available. This updated database allowed the County to maximize credit for controlled impervious surface, which was critical in addressing Municipal Separate Storm Sewer System (MS4) National Pollutant Discharge Elimination System (NPDES) permit requirements related to the Chesapeake Bay Total Maximum Daily Load (TMDL) study.

The Challenge

As part of MS4 permit requirements to help address the Chesapeake Bay TMDL, the Maryland Department of the Environment requires jurisdictions to develop plans to “restore” uncontrolled impervious surface through the implementation of stormwater BMPs. Determining the area that is already controlled by stormwater BMPs is important, because the more area that can be demonstrated as already controlled, the smaller the area that must be retrofitted to meet permit requirements.

Therefore, ensuring that existing BMPs can be “credited” through complete, accurate, and up-to-date documentation was critical to Anne Arundel County. The County faced several challenges in using its BMP data, including inconsistent or lack of data documentation; changes in design requirements, credits and the type of data collected over time; and differences in the data needed for local and State uses.

The Solution

LimnoTech supported Anne Arundel County in updating its BMP database to create a complete, accurate, and up-to-date dataset. Because the County did not have a comprehensive data platform for all of its BMP information (different pieces of BMP data were spread throughout different County programs, depending on those programs’ needs and data collection activities), LimnoTech’s first step was to compile existing BMP data from multiple data sources into one comprehensive database.

Next, we reviewed approximately 8,600 grading permits from 1976 to the present to check the original source of the data against the database. This resulted in the update of approximately 26,000 BMP records. The information recorded and tracked included BMP type and location, drainage area, rainfall depth and water quality volume treated, milestone dates (e.g., build date, inspection dates, etc.), and other critical pieces of information. We also developed solutions for several data problems, including filling in data gaps, tracking modifications to drainage areas over time, and different data scales.

To complete this work, we used the Quick Base data management platform. We used the data application for the permit-related data and a linked GIS geodatabase for the spatial drainage area delineations. The use of Quick Base provided easy access through a web browser. The Quick Base platform also allowed multiple users to work on the data simultaneously, and made it easy to track progress and share results with Anne Arundel County. With this data management system, we were able to set-up internal quality control and logic checks; implement a data logic to calculate critical values missing in the data; and generate reports that were used to answer questions, summarize results, and track progress.

The resulting database reflects an improved and more accurate record of stormwater BMPs in Anne Arundel County. Anne Arundel County intends to use the BMP data in an upcoming MS4 permit re-application to ensure the baseline impervious area controlled is maximized and that future regulatory requirements are based on the most accurate and up-to-date data available. Anne Arundel County will also include the complete and accurate BMP dataset as part of its MS4 annual report to ensure that it maximizes the pollutant load reduction credit for existing BMPs.


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