COMPILATION AND REVIEW OF NATIONWIDE MS4 STORMWATER QUALITY DATA

The University of Alabama and the Center for Watershed Protection were awarded an EPA Office of Water 104(b)3 grant in 2001 to collect and evaluate stormwater data from a representative number of NPDES (National Pollutant Discharge Elimination System) MS4 (municipal separate storm sewer system) stormwater permit holders. The initial version of this database, the National Stormwater Quality Database (NSQD, version 1.0) is currently being completed. These data are being collected and reviewed to describe the characteristics of this data, to provide guidance for future sampling needs, and to enhance local stormwater management activities in areas having limited data.The cumulative value of the monitoring data collected over nearly a ten-year period from more than 200 municipalities throughout the country has a great potential in characterizing the quality of stormwater runoff and comparing it against historical benchmarks. This project is creating a national database of Phase 1 stormwater monitoring data, providing a scientific analysis of the data, and providing recommendations for improving the quality and management value of future NPDES monitoring efforts.Each data set is receiving a quality assurance/quality control review, based on reasonableness of data, extreme values, relationships among parameters, sampling methods, and a review of the analytical methods. The statistical analyses is being conducted at several levels. Probability plots are used to identify range, randomness and normality. Clustering and principal component analyses are also being utilized to characterize significant factors affecting the data patterns. The master data set is also being evaluated to develop descriptive statistics, such as measures of central tendency and standard errors. We are testing for regional and climatic differences, the influences of land use, and the effects of storm size and season, among other factors. This paper describes our data collected to date and presents some preliminary data summaries.When this National Stormwater Quality Database (NSQD) is completed (populated with most of the NPDES stormwater monitoring data), the continued collection of outfall stormwater quality data in the U.S. for basic characterization purposes may have limited use. Some communities may have obviously unusual conditions, or adequate data may not be available in their region. In these conditions, outfall monitoring may be needed. However, stormwater monitoring will continue to be needed for other purposes in many areas having, or anticipating, active stormwater management programs (especially when supplemented with other biological, physical, and hydrologic monitoring components). These new monitoring programs should be designed specifically for additional objectives, beyond characterization. These may include receiving water assessments to understand local problems, source area monitoring to identify critical sources, treatability tests to verify performance of stormwater controls for local conditions, and assessment monitoring to verify success of local stormwater management approach (including model calibration and verification). In many cases, the resources being spent for outfall monitoring could be more effectively spent to better understand many of these other aspects of an effective stormwater management program.