PPP
Indicates a study that has met the very thorough guidelines established and for studies that have been included in the International Stormwater BMP Database
.
PP
Indicates a study that has been published in scientific texts, journals, web sites, grant projects, and presentations. These studies were collected for inclusion in California's draft BMP performance database, MP Miner.
P
Not currently utilized.
In addition to these broad categories, users should examine the details of the study to determine, where available, the number of storm events sampled, the number of samples taken in each storm event, the monitoring methods used, etc. (see Statistical Abstracts)
Statistical Abstracts: For many of the studies from the International Stormwater BMP
Database (PPP), a detailed statistical abstract is available. This abstract presents important details on the
statistical reliability of the information in the study. Users should refer to this summary to gauge the
reliability and statistical variability of the results of the study. These abstracts provide a full range
of statistical information, including confidence intervals, coefficients of variation, standard deviations,
and more.
Inflow and Outflow Concentrations: Where available, the mean or average inflow and outflow concentrations are presented in common units, such as milligrams or micrograms per liter. Studies from the International BMP Database (PPP) present the estimated arithmetic mean of the event mean concentration (EMCs) (which, in plain English, is the average pollutant concentration measured over multiple storm events).
Volume Information: Some of the studies present volume information, including the total measured volume of stormwater coming into the BMP and total volume leaving the BMP. The volume information is restricted to "paired" events, where volume was measured both incoming and outgoing for the same storm event. The volumes are reported in thousands of liters. The volumes vary highly based on the number of storm events that were monitored and the size of those storm events.
Why do some studies show negative volume reduction (e.g., the outgoing volume is higher than the incoming)? There are a variety of reasons why this might happen. First, there could be errors in how volume was measured. Second, the BMP may be discharging shallow ground water in addition to measured surface flows. Another possible reason could be that stormwater is entering the BMP from locations other than the inflow measurement location or stormwater is falling on the BMP directly and is not being measured.
Other Reported Measures of Performance: Some studies do not report the inflow and outflow concentrations of a particular pollutant, but do report a measure, such as "percent removal or effectiveness," which is an unreliable measure of BMP performance (see Why Percent Removal is a Poor Measure of BMP Performance). None-the-less, these studies have been included in the tool because they may contain valuable information on a particular BMP. It is recommended that users not rely solely on such measures, but investigate the details of the study for more information.
