U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007–1213

Prepared in cooperation with the STATE OF HAWAII DEPARTMENT OF TRANSPORTATION

Rainfall, Streamflow, and Water-Quality Data During 

Stormwater Monitoring, Halawa Stream Drainage Basin, 

Oahu, Hawaii, July 1, 2006 to June 30, 2007
This page left intentionally blank
Rainfall, Streamflow, and Water-Quality 

Data During Stormwater Monitoring, 

Halawa Stream Drainage Basin, Oahu, 

Hawaii, July 1, 2006 to June 30, 2007

By Stacie T.M. Young and Marcael T.J. Jamison

Prepared in cooperation with the

STATE OF HAWAII DEPARTMENT OF TRANSPORTATION

Open-File Report 2007–1213

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS--the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Young, Stacie T.M., Jamison, Marcael, T.J., 2007, Rainfall, Streamflow, and Water-Quality Data During Stormwater 

Monitoring, Halawa Stream Drainage Basin, Oahu, Hawaii, July 1, 2006 to June 30, 2007: U.S. Geological Survey 

Open-File Report 2007–1213, 23 p.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Data-Collection Network..............................................................................................................................1

Water-Quality Sampling Techniques ..........................................................................................................2

Sampling requirements........................................................................................................................2

Storm criteria.........................................................................................................................................2

Sample collection .................................................................................................................................2

Determination of discharge for samples ..........................................................................................4

Sample processing, analysis, and quality assurance/quality control .........................................5

Rainfall and Streamflow Data......................................................................................................................5

Stormwater Sampling: Conditions And Results........................................................................................5

Third Quarter 2006 – July 1 to September 30, 2006 .........................................................................6

Fourth Quarter 2006 –October 1 to December 31, 2006 ..................................................................6

Storm of November 1, 2006 ........................................................................................................6

First Quarter 2007 – January 1 to March 31, 2007 .........................................................................12

Second Quarter 2007 – April 1 to June 30, 2007 ...................................................................12

Storm of June 5, 2007 ................................................................................................................12

Quality Assurance........................................................................................................................................16

References Cited..........................................................................................................................................16

Appendix A: Discharge-Reporting and Load-Calculation Methods...................................................17

Appendix B: Physical Properties, Concentrations, and Loads for All Samples Collected from 

Halawa Stream Drainage Basin During the Period from July 1, 2006 to June 30, 2007, 

Oahu, Hawaii...................................................................................................................................18

Figures

1. Stream-gaging stations, rain gages, and water-quality sampling stations in the

Halawa drainage basin, Oahu, Hawaii......................................................................................3

2. Rainfall and discharge for stations within the Halawa Stream drainage basin, Oahu,

Hawaii, for July 1, 2006 to June 30, 2007...................................................................................7

3. Discharge at Storm drain C (212353157533001), Xeriscape garden (16226200), and

Quarantine stations (16226400) for July 1 to September 30, 2006, Oahu, Hawaii...............8

4. Discharge at Storm drain C station (212353157533001) for October 1 to December

31, 2006; detail of 4-hour period of November 1, 2006; and detail of the 1-hour period

from 03:00 to 04:00 November 1, 2006, Oahu, Hawaii..............................................................9

5. Stream discharge at Xeriscape garden station (16226200) for October 1 to

December 31, 2006; detail of 1-day period of November 1, 2006; and detail of the

2-hour period from 04:00 to 06:00 November 1, 2006, Oahu, Hawaii...................................10

6. Stream discharge at Quarantine station (16226400) for October 1 to December 31,

2006; detail of 1-day period of November 1, 2006; and detail of the 4-hour period

from 04:00 to 08:00 November 1, 2006, Oahu, Hawaii............................................................11

7. Discharge at Storm drain C (212353157533001), Xeriscape garden (16226200), and 

Quarantine stations (16226400) for January 1 to March 31, 2007, Oahu, Hawaii .............13
iv

8. Stream discharge at Xeriscape garden station (16226200) for April 1 to June 30,

2007; detail of 1-day period of June 5, 2007; and detail of the 5-hour period from

00:00 to 05:00 June 5, 2007, Oahu, Hawaii...............................................................................14

9. Stream discharge at Quarantine station (16226400) for April 1 to June 30, 2007 and

detail of 1-day period of June 5, 2007, Oahu, Hawaii............................................................15

Tables

1. Minimum reporting levels of properties and constituents for all samples collected

from Halawa Stream drainage basin from July 1, 2006 to June 30, 2007,

 Oahu, Hawaii ................................................................................................................................6

2. Significant figures and rounding limits for measured, streamflow-rating, and

averaged discharges .................................................................................................................17

3. Conversion factors for computing daily loads from constituent concentration and

discharge .....................................................................................................................................17

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

Vertical coordinate information is referenced to mean sea level.

Horizontal coordinate information is referenced to Old Hawaiian Datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).
Abstract

Storm runoff water-quality samples were collected as part 

of the State of Hawaii Department of Transportation Stormwater Monitoring Program. This program is designed to assess 

the effects of highway runoff and urban runoff on Halawa 

Stream. For this program, rainfall data were collected at two 

stations, continuous streamflow data at three stations, and 

water-quality data at five stations, which include the two continuous streamflow stations. This report summarizes rainfall, 

streamflow, and water-quality data collected between July 1, 

2006 and June 30, 2007.

A total of 13 samples was collected over two storms 

during July 1, 2006 to June 30, 2007. The goal was to collect 

grab samples nearly simultaneously at all five stations and 

flow-weighted time-composite samples at the three stations 

equipped with automatic samplers. Samples were analyzed 

for total suspended solids, total dissolved solids, nutrients, 

chemical oxygen demand, and selected trace metals (cadmium, chromium, copper, lead, nickel, and zinc). Additionally, 

grab samples were analyzed for oil and grease, total petroleum 

hydrocarbons, fecal coliform, and biological oxygen demand. 

Quality-assurance/quality-control samples were also collected 

during storms and during routine maintenance to verify analytical procedures and check the effectiveness of equipmentcleaning procedures.

Introduction

The State of Hawaii Department of Transportation 

(DOT) Stormwater Monitoring Program Plan (State of Hawaii 

Department of Transportation Highways Division, 2006) 

was implemented on January 1, 2001 to monitor the Halawa 

Stream drainage basin, Oahu, Hawaii. The Stormwater Monitoring Program Plan was designed to fulfill part of the permit 

requirements for the National Pollutant Discharge Elimination System program and is revised yearly. The Stormwater 

Monitoring Program Plan includes the collection of rainfall, 

streamflow, and water-quality data at selected stations in the 

Halawa Stream drainage basin.

This report summarizes water-quality data collected by 

the U.S. Geological Survey (USGS) as part of the Stormwater 

Monitoring Program Plan. This report also presents rainfall 

and streamflow data collected from July 1, 2006 to June 30, 

2007. Descriptions of the sampling techniques are included 

with the water-quality data.

Two storms were sampled during the period of July 1, 

2006 to June 30, 2007. A total of 13 samples was collected 

during the two storms. In addition, 3 quality-assurance/quality-control (QA/QC) samples were collected: 2 samples were 

collected concurrently with storm samples and 1 sample was 

collected between storms during routine cleaning of the sampling equipment. Water-quality data for the QA/QC samples 

are not published in this report, but are available upon request 

from the USGS Pacific Islands Water Science Center in Honolulu, Hawaii.

Data-Collection Network

Stream-stage, stream-discharge, rainfall, and water-quality data were collected at selected stations in the Halawa 

Stream drainage basin (fig. 1). Rainfall data were collected 

at two stations, 212428157511201, North Halawa Valley rain 

gage at H-3 tunnel portal (abbreviated to Tunnel rain gage) 

and 212304157542201, North Halawa rain gage near Honolulu (abbreviated to Xeriscape garden rain gage). Rainfall data 

have been collected at the Tunnel and Xeriscape garden rain 

gages since July 1998 and May 1983, respectively.

Streamflow data were collected at three stations in North 

Halawa Valley since 1998, 1983, and 2001, respectively 

for station 212353157533001, Storm drain C; and streamflow-gaging stations 16226200, North Halawa Stream near 

Honolulu ( abbreviated to Xeriscape garden); and 16226400, 

North Halawa Stream at Quarantine Station (abbreviated to 

Quarantine). Storm drain C, Xeriscape garden, and Quarantine 

stations are equipped with automatic samplers. The Quarantine 

station gagehouse and equipment were destroyed on December 7, 2003 and rebuilt in June 2005.

Rainfall and streamflow data were collected using variable sampling intervals depending on rainfall or streamflow 

Rainfall, Streamflow, and Water-Quality Data During 

Stormwater Monitoring, Halawa Stream Drainage Basin, 

Oahu, Hawaii, July 1, 2006 to June 30, 2007

By Stacie T.M. Young and Marcael T.J. Jamison
rates. Data from the two rain gages and the two streamflowgaging stations are transferred to the USGS National Water 

Information System (NWIS) database using cellular-phone. 

Data from Quarantine station are transferred to the NWIS 

database hourly via satellite telemetery. Recent data can be 

viewed at http://hi.water.usgs.gov/ under “Real-Time Data 

(from NWISWeb)” by selecting “Streamflow” or “Rainfall”, 

and then selecting the approriate USGS station numbers. Historic rainfall and streamflow data can be accessed through the 

website http://hi.water.usgs.gov/ under “Historical Data (from 

NWISWeb)” by selecting “Streamflow” or “Rainfall” and 

then selecting “Daily Data” and then entering the appropriate 

USGS station numbers.

Water-quality data were collected at five stations (fig. 

1): 212356157531801, North Halawa Stream at Bridge 8 near 

Halawa (abbreviated to Bridge 8); Storm drain C; Xeriscape 

garden; Quarantine; and 16227100, Halawa Stream below H-1 

(abbreviated to Stadium). The Bridge 8 station is about 0.75 

mi upstream from the discharge point of Storm drain C on 

North Halawa Stream. Storm drain C collects runoff from an 

approximately 4-mi length of freeway starting at the leeward 

tunnel portal and extending to mid-valley and discharges 

directly to North Halawa Stream (fig. 1). The Xeriscape 

garden station is directly upstream from a light-industrial area 

near North Halawa Stream, and about 0.75 mi downstream of 

the discharge point of Storm drain C. The Quarantine station 

is about 1 mi downstream of Xeriscape garden and near the 

downstream end of the light-industrial area that borders the 

North Halawa Stream. The Stadium station is about 1.5 mi 

downstream of the Quarantine station downstream from the 

confluence of North and South Halawa Streams, downstream 

from the crossing of H-1 freeway, and directly upstream from 

the mouth at Pearl Harbor. Water-quality data have been 

previously collected at stations Storm drain C (1998-present), 

Xeriscape garden (1983-present), and Stadium (1988-present) 

by the USGS as part of the H-3 freeway construction monitoring study and can be viewed website http://hi.water.usgs.gov/

under “Historical Data (from NWISWeb)” by selecting “Water 

Quality” and then selecting either “Field/lab samples” or 

“Daily Data” and then entering the appropriate USGS station 

numbers.

Water-Quality Sampling Techniques

Water-quality samples include grab samples collected 

manually; grab samples collected by an automatic sampler, 

and flow-weighted time-composite samples collected by 

an automatic sampler. Each grab and composite sample is 

assigned a median sampling time based on the start and finish 

time of the grab sampling process, or the times of collection of 

the sample bottles used for the grab or composite sample from 

the automatic sampler.

Sampling requirements

The DOT Stormwater Monitoring Program Plan states 

that water-quality samples will be collected at least once per 

quarter during periods of storm runoff from each of the five 

water-quality monitoring stations (fig. 1). The plan also states 

that efforts will be made to sample all five water-quality monitoring stations during the same storm, and if a storm does not 

occur during a quarter, no samples will be collected.

A complete set of samples for a storm consists of five 

grab samples (one from each of the five stations), three flowweighted time-composite samples (one each from Storm 

drain C, Xeriscape garden, and Quarantine stations), and one 

QA/QC sample. However, some storms are brief and do not 

produce adequate runoff to sample all five stations and collect 

all samples. In practice, these storms have been sampled as 

thoroughly as possible and analyzed for as many constituents 

as practical.

Storm criteria

The U.S. Environmental Protection Agency’s (USEPA) 

Storm Water Sampling Guidance Manual (U.S. Environmental 

Protection Agency, Office of Water, 1993) provides criteria 

for stormwater-sampling. The first criterion requires at least 

0.1 in. of accumulated rainfall within a storm event. Rainfall 

accumulations have exceeded 0.1 in. at the Tunnel rain gage 

and Xeriscape garden rain gage when stormwater sampling 

was conducted. The second criterion requires that samples be 

collected only for storms preceded by at least 72 hours of dry 

weather. The second criterion would prevent sampling of most 

storms on North Halawa Stream because the Halawa Stream 

drainage basin, as well as many other parts of Oahu, receives 

tradewind showers almost daily.

In practice, criteria used to initiate sampling of the stream 

and storm drain were based on the rate of rainfall accumulation and the rise of stage in Storm drain C, Xeriscape garden, 

and Quarantine stations. Each automatic sampler is triggered 

at predetermined, station-specific, stream-stage thresholds.

Sample collection

In general, grab samples were collected manually using 

isokinetic, depth-integrating samplers and equal-width increment (EWI) or single vertical sampling techniques (Wilde and 

others, 1998). Samplers are made of high-density polyethylene 

(HDPE) that collect water in an isokinetic manner, in which 

water enters the sampler at the same velocity as the stream at 

the sampling point.

The EWI sampling technique utilizes evenly spaced 

sampling increments along the cross section of the stream. The 

volume of sample collected at each increment is proportional 

to the discharge at that increment. Samples collected at each 

increment are combined in an HDPE churn. An EWI sample 

is practical when depths are greater than 0.5 ft and the stream 

   Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
Figure 1. Stream-gaging stations, rain gages, and water-quality sampling stations in the Halawa drainage basin, Oahu, Hawaii.

South Halawa Str

Halawa Str

North Halawa Str

Moanalua Str East Loch

PEARL HARBOR

KANEOHE

BAY

212304157542201

771.9

Xeriscape Garden

Rain Gage

16226400QuarantineStation

212353157533001Storm Drain C

212356157531801Bridge 8

16226200XeriscapeGarden

212428157511201

771.11Tunnel

Rain Gage

HALAWA DRAINAGEBASIN BOUNDARY

212304157542201

771.9

Xeriscape Garden

Rain Gage

16226400QuarantineStation

212353157533001Storm Drain C

212356157531801Bridge 8

21 ̊22'21 ̊26'

157 ̊56' 157 ̊52' 

0

0

2 3 MIL

2 3 KILOMETERS

1

1

H-3 Fwy

STREAM-GAGING AND

WATER-QUALITY STATION,

STATION NUMBER, ANDABBREVIATED NAME (grab andtime-composite sampling)

RAIN GAGE, STATION NUMBER,

STATE KEY NUMBER, ANDABBREVIATED NAME

WATER-QUALITY STATION,

STATION NUMBER, ANDABBREVIATED NAME (grab-onlysampling)

TRANS-KOOLAU

TUNNEL

KOOLAU

CREST

EXPLANATION

Kamehameha

H-1 Fwy

Moanalua

Fwy Likelike Hwy

Pali

Hwy

Ford

Island

16226200XeriscapeGarden

16227100Stadium

16226200XeriscapeGarden

212428157511201

771.11Tunnel

Rain Gage

212428157511201771.11TunnelRain Gage

212356157531801Bridge 8

HALAWA STREAM DRAINAGEBASIN BOUNDARY

Area of

Map

OAHU,

HAWAII

Pacific

Ocean
is wadeable. During storms with high discharge, streams were 

not waded for safety reasons. However, if the stream appears 

to be sufficiently well mixed during high-discharge storms at 

each station, use of the EWI method would not be necessary. 

At such times, a grab sample was collected with the isokinetic 

sampler at the estimated centroid of flow of a single vertical 

section in the stream. Sub-samples from the single-vertical 

technique were combined in a HDPE churn.

A flow-weighted, time-composite sample is created by 

combining, in a HDPE churn, all or part of the samples collected by the automatic samplers. The desired volume of water 

from each sample is proportional to the volume of stream-discharge between sample-collection times. Composite samples 

were collected over time periods that sometimes lasted several 

hours.

Automatic samplers collect water from a fixed point in 

the stream channel after pre-determined stage thresholds are 

met. The automatic samplers have a capacity of 24, 1-liter 

bottles. When the first threshold has been met, the automatic 

samplers are programmed to collect water samples every two 

minutes for the first five samples, and then every 15 minutes 

for the remaining 19 samples. The first stage thresholds for 

the samplers correspond to discharges of 3, 40, and 30 ft3/s 

for Storm drain C, Xeriscape garden, and Quarantine stations, 

respectively. In order to collect enough water in each sample 

during storms with quick rising and falling stream stages, or 

greater overall flow, a second set of stage thresholds, corresponding to higher discharges, is used to trigger the samplers 

to sample every 7 minutes. These higher stage thresholds correspond to discharges of 16, 90 and 108 ft3/s for Storm drain 

C, Xeriscape garden, and Quarantine stations, respectively.

The first three automatic samples were collected in teflon 

bags and the remaining 21 automatic samples were collected 

in low density polyethylene (LDPE) bags. In storms where 

a composite sample could not be created due to insufficient 

automatic samples (5 samples), the automatic samples collected in teflon bags were analyzed for oil and grease (O+G) 

and total petroleum hydrocarbon (TPH). No other constituents would be analyzed due to low sample volume. In storms 

where a manual grab sample could not be collected or the first 

automatic samples are representative of the first rise of the 

stage and flow, the automatic samples collected in teflon bags 

would be used for O+G and TPH analyses and the remaining automatic samples would be combined to be analyzed for 

total suspended solids (TSS), total dissolved solids (TDS), 

nutrients, chemical oxygen demand (COD), and selected trace 

metals (cadmium, chromium, copper, lead, nickel, and zinc). 

Fecal coliform (FC) and biological oxygen demand (BOD) 

would not be analyzed in this case because the “holding times” 

for these constituents would likely be exceeded.

The main limitation associated with using samples from 

the automatic sampler to replace grab samples is that some 

constituents require the sample to be chilled prior to analysis 

or analyzed within a certain time after collection, known as 

the holding time. The automatic samplers were not equipped 

with refrigeration units, and thus holding times for selected 

constituents can be exceeded. Additionally, the automatic 

samplers can decrease the concentration of constituents if the 

constituent bonds to the teflon tubing of the intake line and the 

silicon tubing of the peristaltic pump. Nutrient, FC, and BOD 

analyses would be the most susceptible to holding time and 

refrigeration problems, whereas O+G and TPH analyses are 

the most susceptible to problems associated with the constituent bonding to tubing.

Some storms are difficult to sample due to the timing 

and distribution of discharge. Situations in which the storm 

samples deviate from the sampling requirements outlined in 

the sampling plan occurred when there were multiple peaks in 

discharge, if stream discharge had decreased too much after a 

storm to collect a grab sample, or if a small peak in discharge 

was followed by a much larger peak discharge. In these cases, 

deviation from the sampling requirements include: (1) one or 

more grab samples will be made from the samples collected 

by the automatic sampler, or (2) a composite sample will be 

made from fewer than 24 samples if a gap of a few or more 

hours elapse between the times at which the samples from the 

automatic sampler were collected.

Determination of discharge for samples

At Bridge 8, Storm drain C, Xeriscape garden, and Quarantine stations, discharge associated with each sample was 

determined using a streamflow rating, created for the station, 

or by direct measurement using a current meter. Streamflow 

ratings were developed using measurements and results from 

hydraulic models that were verified by subsequent measurements. At the Stadium station, the wide and curving concretelined channel and shallow and swift streamflow preclude 

development of an accurate streamflow rating. When possible 

discharge at this station was measured using a current meter. 

At higher flows, discharge was measured either by using floatmeasurement techniques or a radar gun. The float-measurement technique involves timing floating bottles over a known 

distance to determine water velocity. The radar gun measures 

surface velocity at multiple points in the cross section. In both 

techniques, the area of the cross section was estimated using 

measured water depths and surveyed dimensions of the channel. USGS practices for making discharge measurements and 

streamflow ratings can be found in Rantz and others (1982).

An average-discharge value was calculated for each 

composite sample. The average-discharge value was equal to 

the total volume of water that flowed by the gaging station 

during sample collection, divided by the total elapsed time 

required to collect the automatic samples. To determine the 

volume of water that passed the station for each sample, the 

discharge at the time of sample collection was multiplied by 

the elapsed time. The elapsed time is computed by taking the 

difference between the times of the samples taken before and 

after the sample in questions and dividing by two. To compute 

the elapsed time of the first and last samples, the difference 

between the time of the sample and next/previous sample is 

 Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
divided by two. These volumes were summed, and the total 

volume was divided by the sum of all the time increments. A 

similar method, the mid-section method, is used when computing the width between sections in discharge measurments is 

described in Rantz and others (1982, P.80).

Measured, streamflow-rating, and averaged discharge 

values are reported to appropriate number of significant figures. These discharge values and the corresponding values of 

constituent concentration are used to compute loads. Reported 

discharge values and the calculation of loads are discussed in 

appendix A.

Sample processing, analysis, and quality 

assurance/quality control

USGS water-quality sampling methods (Wilde and others, 1998) were followed to prevent possible contamination 

during sample processing. Both grab and composite samples 

were processed using churns to mix and suspend sediment 

while delivering the sample to specific bottles for the various 

constituent analyses. The time assigned to each grab and composite sample is the median time of the sample collection.

As required by the DOT Stormwater Sampling Program 

Plan, each composite and grab sample was analyzed for 

temperature, pH, specific conductance, TSS, TDS, nutrients, 

COD, and selected trace metals (cadmium, chromium, copper, 

lead, nickel, and zinc). Chromium and nickel were added 

to the analyses starting in July 2004. Each grab sample was 

also analyzed for O+G, TPH, FC, and BOD. USGS personnel made field measurements of temperature, pH, and specific 

conductance. The minimum reporting levels for each of the 

analyzed properties and constituents are listed in table 1 and 

are based on values published by the USGS National Water 

Quality Laboratory (NWQL). Calculated values, organic 

nitrogen and total nitrogen, do not have minimum reporting 

levels. More information about minimum reporting levels and 

how they are determined by NWQL can be found in Childress 

and others (1999).

FC and BOD analyses were performed by Aecos Incorporated, a private laboratory on Oahu. QA/QC practices are 

conducted at Aecos Incorporated, but are not published. For 

storm-sample events that occurred on a weekend or holiday, 

no FC or BOD samples were collected because Aecos Incorporated was closed and holding times for these constituents 

would be exceeded.

All other analyses were performed at the USGS NWQL, 

in Denver, Colorado. The methods used for analyses of all 

water-quality constituents and quality-control practices at 

NWQL are documented in Friedman and Erdmann (1982), 

Fishman and Friedman (1989), Pritt and Raese (1992), Patton 

and Truitt (1992), and Fishman (1993).

A duplicate sample, field or laboratory, is required by the 

Stormwater Sampling Program Plan for each storm sample. 

A field duplicate is a sample that is collected concurrently or 

split with a grab sample and the analytical results are used to 

verify the sampling method. A laboratory duplicate is a sample 

that is split into two equal parts during sample processing and 

the results are used to verify the precision of the laboratory. 

Field duplicate QA/QC samples were collected at Xeriscape 

garden and Quarantine stations during the storm of November 

1, 2006. No QA/QC sample was collected for the storm of 

June 5, 2007 due to low sample volume. 

During the period between storms, non-dedicated and 

non-disposable equipment, such as churns, isokinetic samplers, automatic-sampler-intake lines, and teflon automaticsampler bottle liners, were cleaned following procedures in 

Wilde and others (1998). Field-blank samples were collected 

on January 9, 2007. Inorganic blank water (IBW), free of 

inorganic constituents, was passed through the automatic 

sampler and collected. The IBW field-blank samples were 

analyzed for the same inorganic constituents as the storm 

samples.

Rainfall and Streamflow Data

Hydrographs of daily rainfall and daily mean streamflow for the period of July 1, 2006 through June 30, 2007 are 

shown in figure 2. A total of 101.6 in. of rain was recorded 

at the Tunnel rain gage and 23.3 in. of rain was recorded at 

Xeriscape garden rain gage during this period. The highest 

recorded daily rainfall at Tunnel rain gage was 5.2 in. on September 26, 2006 at the Xeriscape garden rain gage was 3.0 in. 

on November 2, 2006.

Halawa Stream is an intermittent stream. At Xeriscape 

garden station, the highest daily mean discharge was 90 ft3/s 

on November 1, 2006. The longest period of zero daily mean 

discharge at this station was from August 9 to September 6, 

2006. For Quarantine station, the highest daily mean discharge 

was 93 ft3/s on November 1, 2006. The longest period of zero 

daily mean discharge at this station was from July 1 to August 

22, 2006. For Storm drain C, the highest daily mean discharge 

was 1.7 ft3/s on September 26, 2006. The longest period of 

zero daily mean discharge at this station was from June 17-24, 

2007.

Stormwater Sampling: Conditions And 

Results

During the period July 1, 2006 through June 30, 2007, six 

storms occurred with sufficient runoff to trigger the automatic 

samplers at the predetermined thresholds at Storm drain C, 

Xeriscape garden and Quarantine stations. Of these storms, 

two were sampled: November 1, 2006 and June 5, 2007. 

Water-quality data presented in this report are provisional and 

subject to revision.

Stormwater Sampling: Conditions And Results 
Third Quarter 2006 – July 1 to September 30, 

2006

Hydrographs of discharge during the third quarter 2006 

for Storm drain C, Xeriscape garden, and Quarantine stations 

are shown in Figure 3. No storms were sampled during this 

quarter. One storm occurred on September 26, 2006 had peak 

discharges that exceeded the sampling thresholds at Storm 

drain C, Xeriscape garden and Quarantine stations (fig. 3). 

However due to the flashiness of flow and rapid decrease in 

stage at Storm drain C and Quarantine stations, a sufficient 

number of automatic samples was not collected in order to create a composite sample that represented the storm.

Fourth Quarter 2006 –October 1 to December 31, 

2006

One storm, on November 1, 2006, was sampled during 

the fourth quarter 2006. A complete set of samples was collected for this storm. 

Storm of November 1, 2006

A total of 2.7 in. of rain was recorded during November 

1, 2006 at the Tunnel rain gage, resulting in sufficient runoff 

for a storm sample to be collected on this day. Hydrographs of 

discharge at Storm drain C, Xeriscape garden and Quarantine 

stations during October 1 to December 31, 2006 are shown in 

figure 4, 5, and 6. Discharges and analyzed constituents are 

shown in appendix B.

Composite samples were collected from Storm drain 

C, Xeriscape garden, and Quarantine stations. Manual grab 

samples were collected from all stations. Beginning and ending composite sample-collection times are displayed on the 

hydrographs in figures 4, 5, and 6. Samples were analyzed for 

all constituents listed in the Stormwater Monitoring Program 

Plan (State of Hawaii Department of Transportation Highways 

Division, 2006). Discharge, laboratory measurements of pH 

and specific-conductance values, constituent concentrations, 

loads for the grab samples, and average loads for the composite samples, are shown in appendix B. 

Table 1. Minimum reporting levels of properties and constituents for all samples collected from Halawa Stream drainage basin 

from July 1, 2006 to June 30, 2007, Oahu, Hawaii

[std., standard; μS/cm, microsiemens per centimeter at 25oC; mg/L, milligrams per liter; oC, degrees Celsius; μg/L, micrograms per liter; --, no minimum 

reporting level, computed value; MPN/100mL, most probable number (of colonies) per 100 milliliters]

Property or constituent Minimum reporting levels

pH 0.1 std. units

Specific conductance 2.6 μS/cm

Temperature 0.5oC

Total suspended solids 10 mg/L

Total dissolved solids 10 mg/L

Total nitrogena --

Organic nitrogenb --

Ammonia dissolvedc 0.02 mg/L

Nitrogen, total organic + ammonia (Kjeldahl) 0.10 mg/L

Nitrogen, nitrite + nitrate dissolved 0.060 mg/L

Phosphorus dissolved 0.04 mg/L

Total phosphorus 0.040 mg/L

Chemical oxygen demand 10 mg/L

Total cadmium 0.018 μg/L

Total chromium 0.8 μg/L

Total copper 1.2 μg/L

Total lead 0.06 μg/L

Total nickel 0.16 μg/L

Total zinc 2 μg/L

Oil and grease 7 mg/L

Total petroleum hydrocarbons 2 mg/L

Biological oxygen demand 1 mg/L

Fecal coliform 2MPN/100mL a

Total nitrogen is calculated by adding nitrogen, total organic+ammonia (Kjeldahl) to nitrogen, nitrite+nitrate, dissolved.

b

Organic nitrogen is calculated by subtracting nitrogen ammonia, dissolved, from nitrogen, total organic+ammonia (Kjeldahl).

c

Ammonia, dissolved is reported as nitrogen

   Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
Figure 2. Rainfall and discharge for stations within the Halawa Stream drainage basin, Oahu, Hawaii, for July 1, 2006 to 

June 30, 2007.

0

2

4

6

8

10

Jul Aug Sep

2006

TUNNEL RAIN GAGE (212428157511201)

Data provisional--subject to revision subsequent to June 12, 2007.

0

2

4

6

8

10

DAILY MEAN DISCHARGE, IN CUBIC FEET PER SECOND

XERISCAPE GARDEN RAIN GAGE (212304157542201)

Data provisional--subject to revision subsequent to May 31, 2007

DAILY RAINFALL, IN INCHES

Oct Nov Dec Jan Feb Mar Apr May Jun

2007

0

1

2

3

4

5

STORM DRAIN C (212353157533001)

Data provisional--subject to revision subsequent to June 6, 2007

0

50

100

150

200

XERISCAPE GARDEN (16226200)

Data provisional--subject to revision subsequent to June 6, 2007

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

2006 2007

0

50

100

150

200

QUARANTINE STATION (16226400)

Data provisional--subject to revision subsequent to June 6, 2007

No data for the periods of November 18-22

and January 5-10.

No data for the period of February 16-21.

Stormwater Sampling: Conditions And Results   
JULY 1 TO SEPTEMBER 30, 2006

DISCHARGE, IN CUBIC FEET PER SECOND

0

100

200

300

400

500

600

XERISCAPE GARDEN (16226200)

July 2006 August 2006 September 2006

0

50

100

150

200

250

STORM DRAIN C (212353157533001)

JULY 1 TO SEPTEMBER 30, 2006

JULY 1 TO SEPTEMBER 30, 2006

0

50

100

150

200

250

QUARANTINE STATION (16226400)

July 2006

July 2006

August 2006

August 2006

September 2006

September 2006

Figure 3. Discharge at Storm drain C (212353157533001), Xeriscape garden (16226200), and Quarantine 

stations (16226400) for July 1 to September 30, 2006, Oahu, Hawaii.

 Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
Figure 4. Discharge at Storm drain C station (212353157533001) for October 1 to December 31, 2006; detail of 4-hour period of 

November 1, 2006; and detail of the 1-hour period from 03:00 to 04:00 November 1, 2006, Oahu, Hawaii.

0

10

20

30

40

October 2006 November 2006 December 2006

STORM DRAIN C (212353157533001)

OCTOBER 1 TO DECEMBER 31, 2006

00:00 01:00 02:00 03:00 04:00

0

10

20

30

40

DISCHARGE

POINT ON HYDROGRAPH AT WHICH

BOTTLE FILLED FOR COMPOSITE

SAMPLE

STORM DRAIN C (212353157533001)

STORM OF NOVEMBER 1, 2006

11/01/2006

DISCHARGE, IN CUBIC FEET PER SECOND

11/01/2006

03:00 04:00

0

10

20

30

40

STORM DRAIN C (212353157533001)

STORM OF NOVEMBER 1, 2006

COMPOSITE SAMPLE

COLLECTED FROM 03:19

TO 03:59, November 1, 2006

NO DATA FROM NOVEMBER 1, 2006

04:00 to NOVEMBER 2, 2006

16:55 hrs

GRAB SAMPLE COLLECTED

AT 10:23 hrs, 0.23 cfs.

Stormwater Sampling: Conditions And Results 
Figure 5. Stream discharge at Xeriscape garden station (16226200) for October 1 to December 31, 2006; detail of 1-day period of 

November 1, 2006; and detail of the 2-hour period from 04:00 to 06:00 November 1, 2006, Oahu, Hawaii.

0

200

400

600

800

1000

1200

October 2006 November 2006 December 2006

XERISCAPE GARDEN (16226200)

OCTOBER 1 TO DECEMBER 31, 2006

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 00:00

0

200

400

600

800

1000

1200

DISCHARGE

POINT ON HYDROGRAPH AT WHICH

GRAB SAMPLE WAS COLLECTED

POINT ON HYDROGRAPH AT WHICH

GRAB SAMPLE WAS COLLECTED

DISCHARGE, IN CUBIC FEET PER SECOND

11/01/2006

11/01/2006

04:00 05:00 06:00

0

200

400

600

800

1000

1200

GRAB SAMPLE COLLECTED

AT 13:32, NOVEMBER 1, 2006

XERISCAPE GARDEN (16226200)

STORM OF NOVEMBER 1, 2006

XERISCAPE GARDEN (16226200)

STORM OF NOVEMBER 1, 2006

COMPOSITE SAMPLE COLLECTED

FROM 04:25 TO 05:50, NOVEMBER 1, 2006

10 Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
Figure 6. Stream discharge at Quarantine station (16226400) for October 1 to December 31, 2006; detail of 1-day 

period of November 1, 2006; and detail of the 4-hour period from 04:00 to 08:00 November 1, 2006, Oahu, Hawaii.

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 00:00

DISCHARGE, IN CUBIC FEET PER SECOND

0

200

400

600

800

1000

1200

1400

1600

DISCHARGE

POINT ON HYDROGRAPH AT WHCIH

GRAB SAMPLE WAS COLLECTED

POINT ON HYDROGRAPH AT WHICH

BOTTLES FILLED FOR COMPOSITE

SAMPLE

QUARANTINE STATION (16226400)

0

200

400

600

800

1000

1200

1400

1600

04:00 05:00 06:00 07:00 08:00

QUARANTINE STATION (16226400)

STORM OF NOVEMBER 1, 2006

STORM OF NOVEMBER 1, 2006

COMPOSITE SAMPLE COLLECTED FROM

04:45 TO 07:47, NOVEMBER 1, 2006

GRAB SAMPLE COLLECTED AT

13:05 NOVEMBER 1, 2006

OCTOBER 1 TO DECEMBER 31, 2006

0

200

400

600

800

1000

1200

1400

1600

QUARANTINE STATION (16226400)

October 2006 November 2006 December 2006

11/01/2006

11/01/2006

Stormwater Sampling: Conditions And Results 11
Bridge 8.--The grab sample was collected using the EWI 

method. The sampling cross section was about 19 ft wide, and 

was sampled at 1.0 ft intervals. A discharge of 93.2 ft3/s was 

measured about 10 minutes after sampling using a current 

meter.

Storm drain C.-- One grab sample was collected at the 

centroid of flow in the storm drain by directly submersing the 

churn. At the time of the grab sample, the discharge was 0.23 

ft3/s (fig. 4). Discharge associated with the grab sample was 

determined using the stage at the median time of the grabsample collection and the streamflow rating for this gage.

Storm drain C sampling and recording instruments 

experienced low power during the storm. The automatic 

sampler stopped after six samples were collected and the 

logger stopped recording at 04:00 hrs on November 1, 2006. 

The automatic samples, that were collected, may not have 

been at peak stages. The automatic sampler collected a total 

of six samples during the storm and all six samples were used 

to create a flow-weighted, time-composite sample. The peak 

discharge was 23 ft3

/s on November 1, 2006 at 03:59. The 

average discharge was computed to be 1.4 ft3/s.

Xeriscape garden.-- One grab sample was collected 

by using the EWI method. The sampling cross section was 

30 ft wide and was sampled at 2 ft intervals. The discharge 

measured was 59.0 ft3/s (fig. 5) using a current meter. A field 

duplicate sample was collected from this site and analyzed for 

nutrients and metals.

The automatic sampler collected a total of 24 samples. 

However, the first 11 automatic samples were collected on 

October 31, 2006 and were omitted. The flow was flashy during the period when these samples were collected and resulted 

in an insufficient number of samples to create a composite 

sample. Automatic samples 12-24 were used to create a flowweighted time-composite. The average discharge was computed to be 464 ft3

/s (fig. 5). The peak discharge was 837 ft3/s 

(05:35) on November 1, 2006.

Quarantine station.--A grab sample was collected at the 

centroid of flow about 4 ft from the left bank at a cross section 

located at the gage. The stream was unwadable at time of sample collection. A field duplicate was submitted and analyzed 

for O+G and TPH only. A stream discharge of 73.0 ft3

/s (fig. 

6) was measured concurrently with sampling using a current 

meter at a cross section located downstream from the gage . 

The automatic sampler collected 24 samples and all were 

used to create a flow-weighted time-composite. The average 

discharge was computed to be 338 ft3/s (fig. 6). The peak discharge was 1,050 ft3

/s on November 1, 2006 at 05:40.

Stadium.--A grab sample was collected using the EWI 

method. The sample cross section was 53 ft wide, and was 

sampled at 1 ft intervals. A stream discharge of 129 ft3

/s was 

measured concurrently with sampling using a current meter.

First Quarter 2007 – January 1 to March 31, 2007

Hydrographs showing discharge during the first quarter 

2007 for Storm drain C, Xeriscape garden, and Quarantine stations are shown in Figure 7. No storms were sampled during 

this quarter. One storm occurred on January 8, 2007, had peak 

discharges that exceeded the sampling thresholds at Xeriscape 

garden and Quarantine stations (fig. 7). However due to the 

flashiness of flow and rapid decrease in stage at Storm drain 

C and Quarantine stations, a sufficient number of automatic 

samples was not collected to create a composite sample that 

represented the storm.

Second Quarter 2007 – April 1 to June 30, 2007

One storm was sampled during the second quarter 2007 

on June 5. A partial set of samples was collected due to lack 

of flow at the time of sampling at all sites. Automatic samples 

were collected at Storm drain C, Xeriscape garden, and 

Quarantine stations. However at Storm drain C, the automatic 

sample stage thresholds were exceeded in the days prior to 

the sampling day which resulted in all 24 automatic samples 

being filled prior to the June 5 storm. A sufficient number of 

automatic samples were collected at Xeriscape garden to create a composite sample. At Quarantine station, the automatic 

sample stage thresholds were exceeded for a short period and 

resulted in three automatic samples being collected. No FC or 

BOD was analyzed since only automatic samples were collected and holding times for these constituents were exceeded.

Storm of June 5, 2007

Xeriscape garden.-- The automatic sampler collected 

a total of 22 samples. The first two automatic samples were 

used to create a grab samples to analyzed for O+G and TPH. 

The remaining 20 automatic samples were used to create a 

flow-weighted time-composite. The average discharge for this 

sample was 86 ft3/s (fig. 8). The peak discharge was 117 ft3/s 

(03:55) on June 5, 2007.

Quarantine station.-- The automatic sampler collected 

three samples. The first two automatic samples were used to 

create grab samples and were analyzed for O+G and TPH. The 

third automatic sample was not used since there was sufficient 

sample volume for the O+G and TPH bottles. The average discharge was computed to be 30 ft3

/s (fig. 9). The peak discharge 

was 44 ft3/s on June 5, 2007 at 07:45.

12 Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
Figure 7. Discharge at Storm drain C (212353157533001), Xeriscape garden (16226200), and Quarantine stations 

(16226400) for January 1 to March 31, 2007, Oahu, Hawaii.

JANUARY 1 TO MARCH 31, 2007

DISCHARGE, IN CUBIC FEET PER SECOND

0

20

40

60

80

100

120

140 XERISCAPE GARDEN (16226200)

January 2007 February 2007 March 2007

0

20

40

60

80

100

STORM DRAIN C (212353157533001)

JANUARY 1 TO MARCH 31, 2007

JANUARY 1 TO MARCH 31, 2007

0

20

40

60

80 QUARANTINE STATION (16226400)

March 2007

March 2007

February 2007

February 2007

January 2007

January 2007

Stormwater Sampling: Conditions And Results 13
Figure 8. Stream discharge at Xeriscape garden station (16226200) for April 1 to June 30, 2007; detail of 1-day period of June 5, 2007; 

and detail of the 5-hour period from 00:00 to 05:00 June 5, 2007, Oahu, Hawaii.

0

20

40

60

80

100

120

140

160

April 2007 May 2007 June 2007

XERISCAPE GARDEN (16226200) Data provisional--subject to revision subsequent to June 6, 2007

APRIL 1 TO JUNE 30, 2007

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00

0

20

40

60

80

100

120

140

160

DISCHARGE

POINT ON HYDROGRAPH AT WHICH

BOTTLE FILLED FOR COMPOSITE SAMPLE

POINT ON HYDROGRAPH AT WHICH

GRAB SAMPLE WAS COLLECTED

DISCHARGE, IN CUBIC FEET PER SECOND

06/05/2007

06/05/2007

00:00 01:00 02:00 03:00 04:00 05:00

0

20

40

60

80

100

120

140

160

GRAB SAMPLE COLLECTED

AT 01:35, JUNE 5, 2007

XERISCAPE GARDEN (16226200)

STORM OFJUNE 5, 2007

XERISCAPE GARDEN (16226200)

STORM OF JUNE 5, 2007

COMPOSITE SAMPLE COLLECTED

FROM 01:45 TO 04:25, JUNE 5, 2007

14  Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
Figure 9. Stream discharge at Quarantine station (16226400) for April 1 to June 30, 2007 and detail of 1-day 

period of June 5, 2007, Oahu, Hawaii.

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00

DISCHARGE, IN CUBIC FEET PER SECOND

0

20

40

60

80

DISCHARGE

POINT ON HYDROGRAPH AT WHICH

GRAB SAMPLE WAS COLLECTED

QUARANTINE STATION (16226400)

STORM OF JUNE 5, 2007

GRAB SAMPLE COLLECTED

AT 03:02, JUNE 5, 2007

APRIL 1 TO JUNE 30, 2007

0

20

40

60

80

QUARANTINE STATION (16226400) Data provisional--subject to revision subsequent to June 6, 2007

April 2007 May 2007 June 2007

06/05/2007

Stormwater Sampling: Conditions And Results 15
Quality Assurance

Field and laboratory quality-assurance procedures were 

implemented as described in the DOT Storm Water Monitoring Program Plan (State of Hawaii Department of Transportation Highways Division, 2006). Three quality-assurance 

samples were collected: two field-duplicate samples were collected during one of the two of the storms, and one inorganicblank-water (IBW) sample was collected between storms 

after routine cleaning of the sampling equipment. Results are 

not published in this report, but are available from the USGS 

Pacific Islands Water Science Center upon request.

All grab-sample-collection and sample processing equipment were cleaned prior to use. The automatic-sampler intake 

lines were cleaned three times during the year at Storm drain 

C, and two times at Xeriscape garden and Quarantine stations. 

The automatic sampler conducts a rinse cycle prior to every 

sample collected. The rinse cycle routine is as follows: (1) 

sample line is first purged by air, (2) water is pumped up the 

line to a sensor located before the pump, (3) water is purged 

out, and (4) the sample is then collected.

IBW field-blank samples from the automatic samplers 

were collected at Storm Drain C on January 9, 2007. Intake 

lines were cleaned prior to the collection of IBW field-blank 

samples. The field-blank samples were analyzed for inorganic 

constituents only, which consisted of nutrients, cadmium, copper, lead, chromium, nickel, and zinc. Results are not published in this report, but are available from the USGS Pacific 

Islands Water Science Center upon request.

Inorganic constituents were detected at levels at or below 

the minimum reporting levels for most constituents, which 

are listed in Table 1. Lead and zinc were detected in the field 

blank collected on January 9, 2007 at concentrations above the 

minimum reporting levels.

References Cited

Childress, C.J.O., Foreman, W.T., Connor, B.F., and Maloney, T.J., 1999, New reporting procedures based on longterm method detection levels and some considerations for 

interpretations of water-quality data provided by the U.S. 

Geological Survey National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 99-193, 19 p.

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments (3d ed.): U.S. Geological Survey Techniques of 

Water-Resources Investigations, book 5, chap. A1, 545 p.

Fishman, M.J., ed., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory-

-Determination of inorganic and organic constituents in 

water and fluvial sediments: U.S. Geological Survey OpenFile Report 93-125, 217 p.

Friedman, L.C., and Erdmann, D.E., 1982, Quality assurance 

practices for the chemical and biological analyses of water 

and fluvial sediments: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 5, chap. A6, 181 p.

Patton, C.J., and Truitt, E.P., 1992, Methods of analysis by the 

U.S. Geological Survey National Water Quality Laboratory-

-Determination of total phosphorus by a Kjeldahl digestion 

method and an automated colorimetric finish that include 

dialysis: U.S. Geological Survey Open-File Report 94-455, 

42 p.

Pritt, J.W., and Raese, J.W., eds., 1992, Quality assurance/

quality control manual National Water Quality Laboratory: 

U.S. Geological Survey Open-File Report 94-708, 26 p.

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow: Volume 1. Measurement of stage and discharge, Volume 2. Computation of discharge: U.S. Geological Survey Water-Supply Paper 2175, 284 p. and 346 p.

Sauer, V.B., 2002, Standards for the analysis and processing of 

surface-water data and information using electronic methods: U.S. Geological Survey Water-Resources Investigations Report 01-4044, 92 p.

State of Hawaii Department of Transportation Highways Division, 2006, Annual storm water monitoring program plan 

2006-2007, 20 p.

U.S. Environmental Protection Agency, Office of Water, 1993, 

NPDES storm water sampling guidance manual, prepared 

by C.K. Smoley, CRC Press, Inc., 165 p.

Wilde, F.D., Radtke, D.B., Gibs, Jacob, and Iwatsubo, R.T., 

1998, National field manual for the collection of waterquality data: U.S. Geological Survey Techniques of WaterResources Investigations, book 9, chap. A4, 114 p.

16 Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
Appendix A: Discharge-Reporting and Load-Calculation Methods

This appendix further defines the methods used for reporting discharge data and constituent-concentration data and the 

methods for calculating constituent loads. Discharge and water-quality-data values are rounded off to the number of significant 

figures that best describe the precision of the measurement.

Discharge data.--Table 2 shows the number of significant figures and rounding limits for the range of discharges used in 

this study. Discharges measured by current meter or float-measurement techniques follow guidelines for measured discharges. 

Discharges determined by streamflow rating or by averaging follow guidelines for daily mean discharges (Sauer, 2002). Measured discharges may have more significant figures because they are considered more precise than averaged discharges.

Table 2. Significant figures and rounding limits for measured, streamflow-rating, and averaged discharges

[ft3/s, cubic feet per second; <, actual value is less than shown; ≥ actual value is greater than or equal to value shown]

Range of discharge 

(ft3/s)

Measured discharge Streamflow-rating and averaged discharges

Significant figures Rounding limit Significant figures Rounding limit

<0.10 2 thousandths 1 hundredths

≥ 0.10 and <1.0 2 hundredths 2 hundredths

 ≥ 1.0 and < 10 3 hundredths 2 tenths

 ≥ 10 and < 100 3 tenths 2 units

≥ 100 3 variable 3 variable

Calculation of loads.--Table 3 shows the conversion factors used for determining constituent loads. Constituent loads for 

all analyses are reported as pounds per day (lbs/day) except for fecal coliform, which is reported as billion colonies per day. 

All loads are the product of constituent concentration multiplied by associated discharge and the appropriate conversion factor 

(equation 1). Concentrations are reported in milligrams per liter (mg/L) or micrograms per liter (μg/L), except for fecal coliform, 

which is reported in most probable number (of colonies) per 100 milliliters (MPN/100 ml). Four significant figures are used for 

the conversion factors; however, the load value is reported with the lesser number of significant figures of the values of concentration and discharge.

Q (C) K = L (1)

Where

 Q = discharge (ft3/

s

)

 C = constituent concentration (mg/

L

, μg/

L

, or MPN/

100ml)

 K = conversion factor

 L = constituent load ( lbs/

day or billion colonies per day)

Table 3. Conversion factors for computing daily loads from constituent concentration and discharge

[mg/L, milligrams per liter; μg/L, micrograms per liter; MPN/100mL, most probable number (of colonies) per 100 milliliters; lbs/day, pounds per day]

Unit of concentration Conversion factora Load unit

mg/L 5.394 lbs/day

μg/L 0.005394 lbs/day

MPN/100mL 0.02447 billion colonies per day

a

All conversion factors are based on discharge in cubic feet per second.

Appendix A: Discharge-Reporting and Load-Calculation Methods 17
Appendix B: Physical Properties, Concentrations, and Loads for All Samples 

Collected from Halawa Stream Drainage Basin During the Period from July 1, 

2006 to June 30, 2007, Oahu, Hawaii

18  Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin
d loads for all samples collected from Halawa Stream drainage basin during the period from July 1, 2006 to June 30, 2007, Oahu, Hawaii

vg., value of average discharge for flow-weighted time-composite samples; Conc., concentration; Load, computed from concentration value and 

nstantaneous loads, loads associated with composite samples are average loads; <, actual value is less than the value shown; , actual value 

ow rating, all others are measured; e, value is estimated; --, not analyzed or measured; composite, flow-weighted time-composite sample;

 per second; mg/L,milligrams per liter; lbs/day, pounds per day; μg/L,micrograms per liter; MPN/100 mL, most probable number (of colonies) per 100 milliliters]

Instant. Avg.

Conc.

(mg/L)

Load

(lbs/day)

Conc.

(mg/L)

Load

(lbs/day)

Conc.

(mg/L as N)

Load

(lbs/day)

12:00 Grab 93.2 7.1 95 22.4 30 15,000 56 28,000 0.31 160

03:40 Composite #7.8 8.2 36 -- <10 <420 28 1,200 e0.20 e8.410:23 Grab #0.23 7.7 147 23.8 <10 <12 93 120 0.59 0.7305:03 Composite #464 1.5 e 21,900 -- 2,160 5,410,000 34 85,000 <5.86 <14,70013:32 Grab 59.0 7.2 93 22.4 51 16,000 51 16,000 0.40 130

06:16 Composite #338 7.6 94 -- 1,810 3,300,000 36 66,000 4.76 8,68013:05 Grab 73.0 6.7 96 22.4 63 25,000 51 20,000 0.45 180

11:29 Grab 129 7.6 93 22.6 106 73,800 59 41,000 0.59 41001:35 Grab #40 -- -- -- -- -- -- -- -- --03:05 Composite #86 7.8 78 -- 122 57,000 70 32,000 1.40 650

03:02 Grab #30 -- -- -- -- -- -- -- -- --

Median time (hh:mm) Sample type

Discharge

(ft3/s)

pH, lab

reporting 

to

nearest 0.1

Specific 

conductance 

(μS/cm at 

25oC)

reporting to 

nearest 

whole 

number

Temperature (oC)

reporting to

nearest 0.5 oC

Total suspended solids Total dissolved solids Total nitrogena
d loads for all samples collected from Halawa Stream drainage basin during the period from July 1, 2006 to June 30, 2007, Oahu, Hawaii--Continued 

vg., value of average discharge for flow-weighted time-composite samples; Conc., concentration; Load, computed from concentration value and 

nstantaneous loads, loads associated with composite samples are average loads; <, actual value is less than the value shown; , actual value 

ow rating, all others are measured; e, value is estimated; --, not analyzed or measured; composite, flow-weighted time-composite sample;

 per second; mg/L,milligrams per liter; lbs/day, pounds per day; μg/L,micrograms per liter; MPN/100 mL, most probable number (of colonies) per 100 milliliters]

Conc.

(mg/L as N)

Load

(lbs/day)

Conc.

(mg/L as N)

Load

(lbs/day)

Conc.

(mg/L as N)

Load

(lbs/day)

Conc.

(mg/L as N)

Load

(lbs/day)

Conc.

(mg/L as P)

Load

(lbs/day)

12:00 Grab  0.19  96 <0.02 <10 0.19 96 0.12 60 <0.04 <2003:40 Composite 0.15 6.3 0.025 1.1 0.17 7.2 e0.03 e1 <0.04 <210:23 Grab  0.19  0.24 <0.02 <0.02 0.19 0.24 0.40 0.50 e0.03 e0.0405:03 Composite  5.8 14,000 <0.02 <50 5.8 15,000 <0.06 <200 e0.02 e5013:32 Grab  0.28  89 <0.02 <6 0.28 89 0.12 38 <0.04 <1006:16 Composite  4.7  8,600 <0.02 <40 4.7 8,600 0.06 100 <0.04 <7013:05 Grab  0.33  130 <0.02 <8 0.33 130 0.12 47 <0.04 <2011:29 Grab  0.45  310 <0.02 <10 0.45 310 0.14 97 <0.04 <30

01:35 Grab -- -- -- -- -- -- -- -- -- --

03:05 Composite  1.3  600 <0.02 <9 1.3 600 0.10 46 e0.02 e9

03:02 Grab -- -- -- -- -- -- -- -- -- --

Median time (hh:mm) Sample Type

Organic nitrogenb Ammonia dissolved Nitrogen, total organic + ammonia Nitrogen, nitrite + nitrate dissolved Phosphorus dissolved
d loads for all samples collected from Halawa Stream drainage basin during the period from July 1, 2006 to June 30, 2007, Oahu, Hawaii--Continued

vg., value of average discharge for flow-weighted time-composite samples; Conc., concentration; Load, computed from concentration value and 

nstantaneous loads, loads associated with composite samples are average loads; <, actual value is less than the value shown; , actual value 

ow rating, all others are measured; e, value is estimated; --, not analyzed or measured; composite, flow-weighted time-composite sample;

 per second; mg/L,milligrams per liter; lbs/day, pounds per day; μg/L,micrograms per liter; MPN/100 mL, most probable number (of colonies) per 100 milliliters]

Conc.

(mg/L as P)

Load

(lbs/day)

Conc

(mg/L)

Load

(lbs/day)

Conc.

(μg/L as Cd)

Load

(lbs/day)

Conc.

(μg/L as Cr)

Load

(lbs/day)

12:00 Grab e0.04 e20 <10 <5,000 <0.02 <0.01 6 3

03:40 Composite e0.03 e1 <10 <400 0.03 0.001 2 0.0810:23 Grab 0.05 0.06 <10 <10 0.02 0.00002 5 0.006

05:03 Composite 2.11 5,280 220 550,000 0.36 0.9 202 50613:32 Grab 0.07 20 <10 <3,000 e0.01 e0.003 9 306:16 Composite 1.86 3,390 170 310,000 0.30 0.55 153 27913:05 Grab 0.10 39 10 4,000 e0.01 e0.004 11 4.3

11:29 Grab 0.14 97 20 10,000 e0.01 e0.007 15 10

01:35 Grab -- -- -- -- -- -- -- --03:05 Composite 0.23 110 60 30,000 0.10 0.046 13 603:02 Grab -- -- -- -- -- -- -- --

Median time (hh:mm) Sample type

Total phosphorus Chemical oxygen demand Total cadmium Total chromium
d loads for all samples collected from Halawa Stream drainage basin during the period from July 1, 2006 to June 30, 2007, Oahu, Hawaii--Continued

vg., value of average discharge for flow-weighted time-composite samples; Conc., concentration; Load, computed from concentration value and 

nstantaneous loads, loads associated with composite samples are average loads; <, actual value is less than the value shown; , actual value 

ow rating, all others are measured; e, value is estimated; --, not analyzed or measured; composite, flow-weighted time-composite sample;

 per second; mg/L,milligrams per liter; lbs/day, pounds per day; μg/L,micrograms per liter; MPN/100 mL, most probable number (of colonies) per 100 milliliters]

Conc.

(μg/L as Cu)

Load

(lbs/day)

Conc.

(μg/L as Pb)

Load

(lbs/day)

Conc.

(μg/L as Ni)

Load

(lbs/day)

Conc.

(μg/L as Zn)

Load

(lbs/day)

12:00 Grab 3.8 1.9 0.11 0.055 3.42 1.72 4 203:40 Composite 5.2 0.22 1.51 0.064 1.50 0.063 26 1.110:23 Grab 5.2 0.0065 0.37 0.00046 1.08 0.0013 13 0.016

05:03 Composite 133 333 9.78 24.5 126 315 143 35813:32 Grab 5.6 1.8 0.23 0.073 5.17 1.65 13 4.106:16 Composite 113 206 8.00 14.6 94.4 172 127 231

13:05 Grab 7.4 2.9 0.40 0.16 6.89 2.71 8 311:29 Grab 9.5 6.6 0.56 0.39 9.11 6.3 11 7.701:35 Grab -- -- -- -- -- -- -- --

03:05 Composite 20.8 9.6 3.34 1.5 9.1 4.2 49.8 2303:02 Grab -- -- -- -- -- -- -- --

Median time (hh:mm) Sample Type

Total copper Total lead Total nickel Total zinc
d loads for all samples collected from Halawa Stream drainage basin during the period from July 1, 2006 to June 30, 2007, Oahu, Hawaii--Continued

vg., value of average discharge for flow-weighted time-composite samples; Conc., concentration; Load, computed from concentration value and 

nstantaneous loads, loads associated with composite samples are average loads; <, actual value is less than the value shown; , actual value 

ow rating, all others are measured; e, value is estimated; --, not analyzed or measured; composite, flow-weighted time-composite sample;

 per second; mg/L,milligrams per liter; lbs/day, pounds per day; μg/L,micrograms per liter; MPN/100 mL, most probable number (of colonies) per 100 milliliters]

Conc.

(mg/L)

Load

(lbs/day)

Conc.

(mg/L)

Load

(lbs/day)

Conc.

(mg/L)

Load

(lbs/day)

Conc.

(MPN/100 mL)

Load

(billion colonies per 

day)

12:00 Grab <7 <4,000 <2 <1,000 <1 <500 600 1,00003:40 Composite -- -- -- -- -- -- -- --

10:23 Grab <7 <9 <2 <2 <1 <1 16,000 90

05:03 Composite -- -- -- -- -- -- -- --

13:32 Grab <7 <2,000 <2 <600 <1 <300 700 1,00006:16 Composite -- -- -- -- -- -- -- --13:05 Grab e4 e2,000 2 800 <1 <400 1,600 2,90011:29 Grab <7 <5,000 2 1,000 <1 <700 2,200 6,900

01:35 Grab e6 e1,000 4 900 -- -- -- --03:05 Composite -- -- -- -- -- -- -- --03:02 Grab e4 e600 2 300 -- -- -- --

 ammonia (Kjeldahl), to nitrogen, nitrite + nitrate, dissolved. If the concentration value of nitrogen, nitrite + nitrate dissolved,

tration value of total nitrogen is reported as the sum of the values shown for nitrogen, total organic + ammonia 

If the concentration value of nitrogen, nitrite + nitrate, dissolved is below the minimum reporting

 than the sum of the values shown for nitrogen, total organic + ammonia and nitrogen, nitrite + nitrate dissolved,

a, dissolved, from total organic + ammonia (Kjeldahl). If the concentration value of nitrogen ammonia, dissolved is below 

c nitrogen is reported as less than or equal to the value of total organic + ammonia (Kjeldahl), which

the concentration value of nitrogen ammonia, dissolved is estimated and below the minimum reporting level,

ference between the values shown for nitrogen, total organic + ammonia (Kjeldahl), and nitrogen ammonia, 

Median time (hh:mm) Sample type

Oil and grease Total petroleum hydrocarbons Biological oxygen demand Fecal coliform
Young and Jamison—Rainfall, Streamflow, and Water-Quality Data During Stormwater Monitoring, Halawa Stream Drainage Basin, Oahu, Hawaii, 

July 1, 2006 to June 30, 2007—Open-File Report 2007–1213