Rainfall, Discharge, and Water-Quality Data During Stormwater Monitoring, July 1, 2008, to June 30, 2009—Halawa Stream Drainage Basin and the H-1 Storm Drain, Oahu, Hawaii

ABSTRACT

Storm runoff water-quality samples were collected as part of the State of Hawaii Department of Transportation Stormwater Monitoring Program. The program is designed to assess the effects of highway runoff and urban runoff on Halawa Stream, and to assess the effects from the H-1 storm drain on Manoa Stream. For this program, rainfall data were collected at three stations, continuous discharge data at five stations, and water-quality data at six stations, which include the five continuous discharge stations. This report summarizes rainfall, discharge, and water-quality data collected between July 1, 2008, and June 30, 2009.

Within the Halawa Stream drainage area, three storms (October 25 and December 11, 2008, and February 3, 2009) were sampled during July 1, 2008, to June 30, 2009. A total of 43 environmental samples were collected during these three storms. During the storm of October 25, 2009, 31 samples were collected and analyzed individually for metals only. The other 12 samples from the other two storms were analyzed for some or all of the following analytes: total suspended solids, total dissolved solids, nutrients, chemical oxygen demand, and selected trace metals (cadmium, chromium, copper, lead, and zinc). Additionally, grab samples were analyzed for some or all of the following analytes: oil and grease, total petroleum hydrocarbons, fecal coliform, and biological oxygen demand. Some grab and composite samples were analyzed for only a partial list of these analytes, either because samples could not be delivered to the laboratory in a timely manner, or an insufficient volume of sample was collected by the automatic samplers. Two quality-assurance/quality-control samples were collected after cleaning automatic sampler lines to verify that the sampling lines were not contaminated.

Four environmental samples were collected at the H-1 Storm Drain during July 1, 2008, to June 30, 2009. An oil and grease sample and a composite sample were collected during the storm on November 15, 2008, and two composite samples were collected during the January 11, 2009, storm. All samples at this site were collected using an automatic sampler. Samples were analyzed for some or all of the following analytes: total suspended solids, nutrients, oil and grease, total petroleum hydrocarbons, and selected trace metals (cadmium, chromium, copper, lead, nickel, and zinc). One qualityassurance/quality-control sample was collected after cleaning automatic sampler lines to verify that the sampling lines were not contaminated.

During the storm of January 11, 2009, the two composite samples collected at H-1 Storm Drain were collected about three hours apart. Higher constituent concentrations were detected in the first 2 composite sample relative to the second composite sample, although the average discharge was higher during the period when the second sample was collected.

First posted August 13, 2009