Copper Roof Stormwater Runoff - Corrosion And The Environment

Experimental Method

The copper content and flow of stormwater runoff was measured at five locations within the 46.5 hectare watershed at the University of Connecticut (UCONN) campus at Storrs, which includes an Alloy C11000 copper roof installed in 1992. Copper concentration in stormwater was also measured on a copper roof installed in 1931 at Trinity College, in nearby Hartford, Connecticut, which resides in another watershed. ISCO 6700 Series Automated Samplers equipped with 24 one-liter bottles were used to collect samples for chemical analysis. At each sampling station, the sampling equipment was housed in a protective box. Flow at a weir across the stream exiting the UCONN watershed was measured with a Wescorp pressure transducer. An ISCO 730 Series Bubble Module and an ISCO Flow Meter insert was used to measure flow at all other locations.

Before each storm, the equipment was activated. Water samples were taken every 30 minutes over an eight-hour period at the weir across the stream during the course of 16 rain events. They were taken at all other locations every 15 minutes for a total of six hours. The samples were collected and the following laboratory measurements were made: total and dissolved Cu, total Ca, total Mg, dissolved organic carbon (DOC) and pH. Several others measurements were also made but are not included in the interest of brevity. Approximately 10% of the unfiltered samples were tested for copper speciation and toxicity.

A Perkins-Elmer Optima XL 3300 Inductivity-Coupled Plasma Atomic Emission Spectroscopy (ICP - AES) equipped with an AS-91 Autosampler was used to measure total copper and dissolved copper (as per EPA Method 6020). It should be noted that the latter EPA method measures all copper after passing through a 0.45 µm filter. This includes fine particles of <0.45 µm which are not truly dissolved since they are in the solid and not in the ionic states. Cupric ion or ionic copper concentration was measured with an Orion Series 9429 cupric ion selective electrode with a Orion Double Reference Electrode (Model 9002). The two electrodes were connected to a Fisher Scientific Accumet pH meter 25 in mV mode. Low levels of cupric ions, below 6µg/L, were measured with a preconditioned selective electrode. Details of the analytical procedure for all measurements are described in detail elsewhere 1.

Acute toxicity testing was conducted by New England Bioassay using the Cladoceran, Daphnia pulex, an aquatic invertebrate which was chosen by DEP because of its sensitivity to copper toxicity and prevalence in the Northeastern United States. Neonatal daphnia, less than 24-hours-old were exposed to undiluted samples. Survival was measured after 48 hours. Acute toxicity tests were performed according to EPA test methods described in EPA/600/4-90/027F, the state of Connecticut toxicity testing protocols (Sections 22a - 430-3 (j) (7) (A) and Connecticut DEP general permit for stormwater discharge associated with industrial activities.

Low-toxicity samples, exhibiting 50% or greater survival after 48 hours, did not undergo further testing. High-toxicity samples were diluted with EPA soft fresh water to determine the copper concentration at which 50% survived after 48 hours, which is known as an LC 50 test.

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