U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2014–5158

Prepared in cooperation with the National Park Service

Baseline Water-Quality Sampling to Infer Nutrient 

and Contaminant Sources at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i, 2009
Cover photograph. Oblique aerial photograph of ʻAimakapā Fishpond at Kaloko-Honokōhau National Historical Park, 

island of Hawai‘i. Aerial photograph by Brian Powers, Hawaiian Images, used with permission.
Baseline Water-Quality Sampling 

to Infer Nutrient and Contaminant 

Sources at Kaloko-Honokōhau 

National Historical Park, Island of 

Hawai‘i, 2009

By Charles D. Hunt, Jr.

Prepared in cooperation with the National Park Service

Scientific Investigations Report 2014–5158

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014

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Suggested citation:

Hunt, C.D., Jr., 2014, Baseline water-quality sampling to infer nutrient and contaminant sources at KalokoHonokōhau National Historical Park, Island of Hawai‘i, 2009: U.S. Geological Survey Scientific Investigations 

Report 2014-5158, 52 p., http://dx.doi.org/10.3133/sir20145158.

ISSN 2328-0328 (online)
iii

Acknowledgments 

The National Park Service at Kaloko-Honokōhau National Historical Park collaborated in 

study design and preparation of the project as part of the Water-Quality Partnership Program between the National Park Service (NPS) and the U.S. Geological Survey (USGS) 

(thanks especially to Sallie Beavers and Tahzay Jones for their contributions). NPS staff 

also assisted with field orientation and logistical assistance during sampling, and provided 

geographic information system (GIS) map layers (thanks to Lisa Marrack, Rebecca Most, 

Paula Cutillo, and others).

The Shores at Kohanaiki granted permission to sample monitoring wells and irrigation 

water on their property and assisted with site access. Thanks to Joe Root and Gregg 

Scheid for coordinating the sampling visits and alerting security staff to allow entry onto the 

property.

The County of Hawai‘i Department of Water Supply granted permission to sample their 

Honokōhau well, provided site access, and ensured that the pump was running during the 

sampling visit. Thanks to Milton Pavao, Clyde Young, Bob Ravenscraft, and Owen Suzuki.

Keith Olson at the Natural Energy Laboratory of Hawai‘i Authority (NELHA) provided data 

from their deep and shallow seawater intake pipes that help constrain saltwater-source 

assumptions for the samples.

Fellow USGS scientists assisted in the week-long field sampling campaigns (Ron Fay in 

July and Adam Johnson in December) and with site reconnaissance and preparation (Jeff 

Perreault, Delwyn Oki). Adam Johnson also conducted ultraviolet (UV) fluorescence tests 

for optical brighteners on the water samples.
iv

Contents

Acknowledgments ......................................................................................................... iii

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

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

Problem...................................................................................................................2

Objectives and Approach ........................................................................................4

Purpose and Scope ................................................................................................4

Environmental Setting and Previous Studies .................................................................6

Surrounding Developments and Water-Quality Concerns for the Park.................10

Previous Studies ...................................................................................................10

Sampling Sites, Field Methods, and Laboratory Analysis.............................................11

Sampling Sites ......................................................................................................11

Field Methods........................................................................................................13

Sample Collection ..........................................................................................13

Quality-Assurance Samples...........................................................................13

Field Measurements of Water Physical Properties ........................................13

Computation of Salinity, Saltwater Fraction, Freshwater Fraction .................13

Laboratory Analysis...............................................................................................14

Recomputation of Reported Nutrient Concentrations ....................................14

Low-Level Detections.....................................................................................15

Stable Isotopes and Isotope Notation ............................................................15

Optical Brighteners.........................................................................................16

Hydrologic and Tidal Conditions During Sampling ................................................20

Results and Interpretation ............................................................................................24

Salinity and Temperature.......................................................................................24

Stable Isotopes of Water.......................................................................................29

Nutrients................................................................................................................29

Nitrogen..........................................................................................................29

Phosphorus....................................................................................................33

Nutrient Implications of the Cold Saline Groundwater ...................................33

Stable Isotopes of Nitrate for Nitrate Source Identification....................................36

Stable Isotopes of Boron.......................................................................................42

Apparent Chlorofluorocarbon Age at the Honokōhau Well....................................42

Pharmaceuticals, Wastewater Compounds, and Volatile Organic Compounds....43

Results for July...............................................................................................43

Results for December ....................................................................................44

Optical Brightener Fluorescence...........................................................................45

Summary and Conclusions...........................................................................................45

Study Limitations and Opportunities for Future Research............................................46

References Cited..........................................................................................................47
v

Figures

1. Map showing location of Kaloko-Honokōhau National Historical Park, 

Island of Hawai‘i, and existing and planned urban developments and 

wells nearby (2010) ..........................................................................................3

2. Photographs showing anchialine pool and endemic shrimp at KalokoHonokōhau National Historical Park, Island of Hawai‘i.....................................4

3. Map showing locations of water sampling sites and age of lava flows 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i.....................5

4. Map showing mean annual precipitation near Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i ........................................................7

5. Photographs showing lava flows of different ages at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i ........................................................8

6. Oblique aerial photograph of ʻAimakapā Fishpond at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i ........................................................8

7. Conceptual models of interconnection among groundwater bodies at 

Kaloko-Honokōhau National Historical Park, Island of Hawai‘i.........................9

8. Schematic cross section showing how fishponds and anchialine pools 

intersect the water table at Kaloko-Honokōhau National Historical Park, 

Island of Hawai‘i................................................................................................9

9. Graph showing nitrate source classification based on nitrogen and 

oxygen stable-isotope compositions of dissolved nitrate................................16

10. Graph showing daily precipitation at Kaloko-Honokōhau Park, Island 

of Hawai‘i, 2007–09 ........................................................................................20

11. Graph showing monthly precipitation at Honokōhau Harbor, Island 

of Hawai‘i, 2000–09 ........................................................................................21

12. Graph showing daily mean water levels at Kawaihae tide gage and

 in monitoring wells KAHO 2 and KAHO 3 at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i ......................................................22

13. Graph showing July 2009 sample collection times at Kaloko-Honokōhau 

National Historical Park in relation to daily tides at Kawaihae tide gage, 

Island of Hawai‘i..............................................................................................23

14. Graph showing December 2009 sample collection times at KalokoHonokōhau National Historical Park in relation to daily tides at 

Kawaihae tide gage, Island of Hawai‘i ............................................................24

15. Graph showing temperature versus salinity for July 2009 water samples 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i...................25

16. Graph showing temperature versus salinity for December 2009 water 

samples at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i ....26

17. Graph showing change in salinity from July to December 2009 at KalokoHonokōhau National Historical Park, Island of Hawai‘i...................................28

 18. Graph showing depth profiles of temperature and specific conductance 

in Kohanaiki monitoring well MW401, Island of Hawai‘i, December 7, 2009, 

and USGS water samples one week earlier on November 30 .......................28

19. Graph showing δ2H versus δ18O for July 2009 water samples at KalokoHonokōhau National Historical Park, Island of Hawai‘i...................................31

20. Graph showing δ2H versus δ18O for December 2009 water samples 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i...................31
vi

21. Graph showing dissolved inorganic nitrogen versus salinity for July 2009 

water samples at Kaloko-Honokōhau National Historical Park, Island 

of Hawai‘i ........................................................................................................32

22. Graph showing dissolved inorganic nitrogen versus salinity for 

December 2009 water samples at Kaloko-Honokōhau National 

Historical Park, Island of Hawai‘i ....................................................................32

23. Graph showing change in dissolved inorganic nitrogen from July to 

December 2009 at Kaloko-Honokōhau National Historical Park, Island 

of Hawai‘i ........................................................................................................34

24. Graph showing orthophosphate versus salinity for July 2009 water 

samples at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i ....34

25. Graph showing orthophosphate versus salinity for December 2009 

water samples at Kaloko-Honokōhau National Historical Park, Island 

of Hawai‘i ........................................................................................................35

26. Graph showing change in orthophosphate from July to December 2009 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i...................35

27. Graph showing δ18O versus δ15N of nitrate for July 2009 water samples 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i...................38

28. Graph showing nitrate versus δ15N of nitrate for July 2009 water samples 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i...................38

29. Graph showing δ18O versus δ15N of nitrate for December 2009 water 

samples at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i ....40

30. Graph showing nitrate versus δ15N of nitrate for December 2009 water 

samples at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i ....40 

31. Graph showing change in δ15N of nitrate from July to December 2009 at 

Kaloko-Honokōhau National Historical Park, Island of Hawai‘i.......................41

32. Graph showing change in δ18O of nitrate from July to December 2009 at 

Kaloko-Honokōhau National Historical Park, Island of Hawai‘i.......................41

Tables

[Tables 3 and 4 available online at http://dx.doi.org/10.3133/sir20145158]

1. Water sampling sites in and around Kaloko-Honokōhau National 

Historical Park, Island of Hawai‘i, July and December 2009 ..........................12

2. Laboratory methods and field measurements for water samples 

collected at Kaloko-Honokōhau National Historical Park, Island of 

Hawai‘i, July and December 2009 ..................................................................14

5. Tests for optical brighteners in water samples collected at KalokoHonokōhau National Historical Park, Island of Hawai‘i, July and 

December 2009 ..............................................................................................17

6. Nitrate stable-isotope compositions of wastewater sources for 

comparison to results of this study .................................................................37
vii

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 25.4x106 nanometer (nm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.4047 hectare (ha)

Volume

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

million gallons (Mgal) 3,785 cubic meter (m3)

Flow rate

gallon per day (gal/d) 0.003785 cubic meter per day (m3/d)

million gallons per day (Mgal/d) 0.04381 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 local mean sea level.

Horizontal coordinate information is referenced to the North American Datum of 1983 

(NAD 83).

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

at 25 °C).

Concentrations of chemical constituents in water are reported either in milligrams per liter 

(mg/L) or micrograms per liter (μg/L), or micromoles per liter (μM/L).

Isotopic compositions are reported in delta notation, in units of per mil (parts per thousand, 

symbol ‰).
This page left intentionally blank.
Abstract 

Baseline water-quality sampling was conducted for 

dissolved nutrients and for chemical and isotopic tracers at 

Kaloko-Honokōhau National Historical Park on the Island of 

Hawai‘i. Existing and future urbanization in the surrounding 

areas have the potential to affect water quality in the Park, and 

so the National Park Service and the U.S. Geological Survey 

designed a water-sampling strategy to document baseline 

conditions against which future changes can be compared. 

Sites in and near the Park were sampled twice, in July and 

December 2009, and included four anchialine pools, two large 

fishponds, five monitoring wells, an upland production well, 

tap water, and a holding pond for golf-course irrigation water. 

Water samples within the coastal park were brackish, ranging 

in salinity from 15 to 67 percent seawater. Samples were analyzed for dissolved inorganic nutrients (nitrogen and phosphorus), stable isotopes (nitrogen and oxygen in dissolved nitrate; 

hydrogen and oxygen in the water molecule), pharmaceuticals, 

wastewater compounds, and volatile organic compounds. A 

case of acute, but temporary, fertilizer contamination was evident along the Park’s north boundary during the turf grow-in 

period of a newly constructed golf course. A maximum nitrogen concentration 280 percent above background level was 

measured in monitoring well MW401 in July, later falling to 

109 percent above background by December. Two nearby sites 

(MW400 and AP 144) had nitrogen concentrations that were 

elevated compared to remaining sites but less severely than at 

MW401. Aside from this localized fertilizer influence, other 

water samples had lower nutrient enrichments: 40 percent 

or less above background for nitrogen and 57 percent or less 

above background for phosphorus. Background was defined in 

this study by a graphical mixing line between saltwater from a 

deep well in the Park and freshwater at a reference well in the 

mountainous uplands (Honokōhau production well, at 1,675 ft 

altitude). Potential nutrient sources between the uplands and 

coastal lowlands that could contribute to enrichment include 

rock weathering, natural vegetation, fertilizers, septic leachate, 

and atmospheric deposition – including motor-vehicle exhaust. 

Some fraction of septic leachate is expected in groundwater 

because there are unsewered suburban and commercial developments upslope from the Park that rely on cesspools and septic systems. However, stable isotopes of nitrate did not implicate septic-waste nitrogen (heavy δ15N values on the order of 

+10 per mil or greater). Instead, the heaviest δ15N values of +6 

to +8 per mil were associated with the large fishponds, likely 

as a result of biotic cycling. Water samples with δ15N values of 

+3 to +5 per mil were still isotopically heavier than the upland 

groundwater value of +2 per mil and likely reflect addition of 

heavier nitrogen, possibly from septic sources, nitrogen-fixing 

vegetation, or vehicular exhaust. Pharmaceuticals, wastewater 

compounds, and volatile organic compounds indicated that if 

contamination is present, it appears to be at low, barely detectable, levels—at least as reflected by the results of this study. 

The most diagnostic indication of septic contamination was at 

monitoring well KAHO 2, closest to Kaloko Light Industrial 

Park, where three pharmaceuticals (carbamazepine, sulfamethoxazole, and thiobendazole) were detected at trace-level 

parts-per-trillion concentrations. A screening-level test for 

laundry fabric brighteners indicated positive detection at most 

sites; however, readings were quite low and if laundry graywater is present, it appears to be a small, dilute fraction. Because 

the weather was persistently dry throughout the study period, 

the USGS team was unable to conduct a wet-weather “storm” 

sampling. Wet-weather results are expected to differ from 

those reported here, though by how much remains unknown.

Introduction

Kaloko-Honokōhau National Historical Park (KAHO, or 

“the Park” as used in this report) is located on the west coast 

of the Island of Hawai‘i near the urban center of Kailua-Kona 

(fig. 1), a popular resort, residential, and commercial center 

in West Hawai‘i. Hotels and condominiums line much of the 

shore in Kailua-Kona, intermixed with suburban bedroom communities of year-round residents. Upland slopes are occupied 

by suburban residential subdivisions and farm homesteads, 

Baseline Water-Quality Sampling to Infer Nutrient 

and Contaminant Sources at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i, 2009

By Charles D. Hunt, Jr.
2

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

large tracts of low-intensity farmland and ranchland, and forest preserves at higher elevations. The area is supported by 

tourism, agriculture, and a service-based economy, with visitors and residents enjoying the warm climate, scenic views, 

and outdoor recreation. The area contains a State harbor that 

hosts an active deep-sea game fishing fleet and several golf 

courses at larger resorts, the closest being at the newly developed Shores at Kohanaiki resort that abuts the Park along its 

northern border.

The 1,160-acre Kaloko-Honokōhau Historical Park 

was established in 1978 “for the preservation, protection and 

interpretation of traditional (N)ative Hawaiian activities and 

culture” (National Park Service, 2014a). The Park supports 

nationally significant natural resources that include more 

than 150 known anchialine pools, two large (11- and 15-acre) 

Hawaiian fishponds with large associated wetlands, and 

596 acres of nearshore marine waters (DeVerse, 2006). 

Water quality and water quantity are vital to the Park’s 

mission. As an example, one of the Park’s goals is to restore 

the Kaloko Fishpond to operate in the ancient, traditional fashion of aquaculture, producing fish for human consumption. 

Park water resources are mainly supplied by groundwater; 

and the anchialine pools and ʻAimakapā Fishpond are solely 

dependent on groundwater and direct precipitation. In contrast, 

the Kaloko Fishpond has an opening in its constructed rock 

wall that allows direct tidal exchange of water with the ocean.

The anchialine pools are rare ecosystems of brackish 

water where low-lying depressions in the terrain intersect 

the water table (fig. 2), which lies just above sea level. Water 

levels fluctuate tidally, but the pools have no direct surface 

connection to the ocean—instead they are hydrologically connected through a permeable aquifer (Holthuis, 1973) by way 

of fractures, voids, and open conduits such as lava tubes.

The anchialine pools support three known candidate 

endangered species – two shrimp (Metabetaeus lohena, Palaemonella burnsi) and a damselfly (Megalagrion xanthomelas) 

(National Park Service, 2014b). ʻAimakapā Fishpond (fig. 1) 

and adjacent wetland is a significant foraging and nesting 

habitat for the two endangered waterbirds, the Hawaiian coot 

(Fulica alai) and the Hawaiian stilt (Himantopus mexicanus 

knudseni), and Kaloko Fishpond (fig. 1) is a foraging site and 

potential nesting site for the Hawaiian stilt. Marine waters 

of the Park provide habitat for the endangered hawksbill 

turtle (Eretmochelys imbricata), the threatened green sea 

turtle (Chelonia mydas), the endangered Hawaiian monk 

seal (Monachus schauinslandi), and the humpback whale 

(Megaptera novaeangliae).

Groundwater near the coast is brackish and not suitable 

for drinking water or household use. Public supplies of drinking water are obtained from deep wells drilled upslope, most 

of these wells are a mile or more inland (fig. 1) above 500 ft 

elevation. Wells nearer the coast provide brackish water that 

is still usable for landscape irrigation, and some resorts have 

begun to desalinate brackish and saline groundwater to meet 

their irrigation needs.

Problem

When Kaloko-Honokōhau Historical Park was established in 1978, lands surrounding the Park were undeveloped 

and zoned for conservation purposes. In the intervening 

decades, land-use planning has allowed northward expansion of the Kailua-Kona urban area to lands surrounding and 

upslope of the Park so that, at present, most of these lands are 

either developed or zoned for industrial, commercial, or residential use (fig. 1). Surrounding developments include a golf 

course, multiple light industrial parks, and residential subdivisions (figs. 1, 3).

The National Park Service is concerned that neighboring 

land uses may have deleterious effects on water quality and 

water availability within the Park. The leading water-quality 

concerns for the Park are the possible migration of nutrients 

and other contaminants into the Park from surrounding areas, 

and potential long-term changes in the salinity of pools and 

ponds that may occur for a number of reasons.

Contaminants or constituents of concern include 

(1) pesticides and fertilizer nutrients from landscaping and 

agriculture; (2) nutrients and wastewater contaminants from 

cesspools and septic systems in industrial and residential 

areas; and (3) urban chemicals in roadway runoff, from spills, 

or from improper disposal. Long-term salinity changes may 

result from (1) relative sea-level rise, the combined effect 

of local island subsidence paired with a global rise in ocean 

levels; (2) long-term climate change that may bring drier 

climate and less groundwater recharge in the Park’s watershed; 

(3) groundwater withdrawal from wells upslope, which would 

capture part of the fresh groundwater flowing shoreward and 

possibly result in altered salinity in the Park; and (4) injection 

of saline water resulting from the desalination process or 

injection of other effluents.
Introduction 3

Figure 1. Map showing location of Kaloko-Honokōhau National Historical Park, Island of Hawai‘i, and existing 

and planned urban developments and wells nearby (National Park Service [NPS], written commun., 2010).

Māmalahoa H gi hway

Queen Ka‘ahumanu Highway

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1

2

3

12

7

8

9

11b 11a

13

14

6

15

Kaloko Fishpond Kaloko Fishpond

‘Aimakap Aimakapā Fishpond Fishpond

Kaloko-Honokōhau 

National Historical 

Park

Kaloko-Honokōhau 

National Historical 

Park 4

5

10

MW401

K01 - K08

Honokōhau 2 (proposed) 

Kamakana 

Keāhole Point 1-12

Kahalu‘u A-D

Dust Control

Keāhole 4461-02

Keāhole-4462-02

Net Washing

Coffee

Honokōhau

Hualālai

Kalaoa A

Keahuola QLT 1 Keōpū

Keōpū-Puʻuhonua

Kohanaiki 2

Palani 1

Wai‘aha

Komo Monitor

Hōlualoa

Kahalu‘u Shaft

Honoköhau Quarry

Kalaoa Keöpü Deep

156°02' 156°00' 155°58'

19°44'

19°42'

19°40'

19°38'

19°36'

EXPLANATION

Park boundary

Coral reef

Anchialine pool

Pumped well

Injection well

Monitoring well

Unused well

Major road

Tax Map Key boundaries

1 ‘O‘oma Beachside Village

2 The Shores at Kohanaiki

3 DLNR

4 DHHL Commercial / Industrial Park

5 Wastewater Treatment Plant

6 Kaloko Makai

7 Kaloko Transitional Housing

8 TSA Industrial Park Phases 3-4

9 Lanihau West Hawai‘i Business Park

10 McClean Properties Increment II

11a Villages of Laiopua

11b Kealakehe Planned Community

12 Queen Lili‘uokalani Trust

13 Keahuolu Housing / Forest City

14 Kula Nei

15 Kaloko Heights

Existing light industrial

0 0.5 1 1.5 2 MILES

0 0.5 1 2 KILOMETERS

156° 155°

20°

19°

Area

of

map

Island of

Hawai‘i

Kailua-Kona

Base from U.S. Geological Survey digital data (2004), 1:24,000, UTM Zone 5, NAD83 datum.
4

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Objectives and Approach

Objectives of this study were to (1) establish a baseline 

of current water-quality conditions while contaminant sources 

to groundwater in the Park are still relatively low; (2) identify 

sources of nutrients, particularly where nutrient concentrations 

are elevated; and (3) use study results to devise a chemical 

and isotopic monitoring strategy for the Park to consider in its 

management plan.

The study approach entailed sampling selected wells, 

ponds, and anchialine pools in and near the Park (fig. 3) in 

July and December 2009. One intended goal of the approach 

was to characterize fair-weather and storm conditions, but 

owing to a lack of rainstorms in the available field period, the 

goal of obtaining a storm sampling was not met (both sampling rounds were essentially fair-weather samplings that fell 

within extended periods of hot, dry weather).

A key element of the study approach was to apply nutrient and wastewater “tracers” that have been used elsewhere in 

Hawai‘i and nationally, but had not been used at the Park. In 

addition to nutrient concentrations (which have been analyzed 

in prior water-quality surveys of the Park), water samples 

were analyzed for nitrogen stable isotopes, organic wastewater 

compounds, pharmaceuticals (also present in wastewater), 

and volatile organic compounds (these include gasoline 

compounds, household and industrial cleaners and solvents, 

and many more chemicals). Concentrations of some of these 

constituents in groundwater may provide insight into possible 

sources that have known characteristic concentrations. For 

example, isotopically heavy nitrogen can indicate a human- or 

animal-waste source of nitrogen. Likely contaminant sources 

can also be inferred indirectly for simpler constituents, for 

example if high nitrogen concentrations in the Park are linked 

by a spatial pattern of even higher concentrations from an 

obvious source outside and adjacent to the Park.

A fundamental goal of the study was to establish a baseline of these tracer constituents now—before urban development intensifies further and water-quality effects of current 

development are allowed more time to manifest. Because 

several urban developments adjacent to and upslope from 

the Park have been in place for a decade or longer, current 

conditions are not equivalent to a “natural” or “predevelopment” baseline. However, results obtained now will provide a 

reference condition for future comparisons aimed at detecting 

water-quality changes that accompany future development and 

further effects of developments already in place.

Purpose and Scope 

The purpose of this report is to convey results of baseline 

water-quality sampling within Kaloko-Honokōhau National 

Historical Park and its nearby environs. The report tabulates 

various chemical constituents and water properties that were 

measured, and it includes graphical presentations and cursory 

interpretations of the data. The degree of interpretation is 

limited by the study design, which was a reconnaissancelevel sampling effort and not a process-level study aimed at 

understanding geochemical cycling in the Park ecosystem 

nor effects of chemicals on park biota. Nevertheless, some 

process-related implications are apparent in the data and are 

discussed where warranted. This study did not determine 

effects on ecosystems of any of the chemicals or physical 

properties measured.

Figure 2. Photographs showing anchialine pool and 

endemic shrimp at Kaloko-Honokōhau National Historical 

Park, Island of Hawai‘i. A, Anchialine pool AP 53H. 

B, Endemic shrimp Halocaridina rubra. Shrimp are 

about 0.5 inch long. Photographs by Delwyn Oki, U.S. 

Geological Survey.

A

B
Introduction 5

)

)

)

)

)

)

)

)

)

)

)

)

)

A45

G18

AP 099

AP 016

MW401 MW400

AP 53H

AP 144

KAHO 3

KAHO 2

KAHO 1

Irrigation

pond

NPS tap water

156°02' 156°01'

19°42'

19°41'

19°40'

0 0.25 0.5 0.75 1MILES

0 0.25 0.5 1 KILOMETERS

Kaloko

Light

Industrial

Park

Kealakehe Wastewater

Treatment Plant

Honokōhau

Harbor

Landfill

Quarry

Kohanaiki Golf

and Ocean Club

Wastewater

disposal

pit

Kaloko

Fishpond

‘Aimakapā

Fishpond

Base from U.S. Geological Survey digital data (2004), 1:24,000, UTM Zone 5, NAD83 datum. Tax Map Key boundaries from Hawaii State Office of Planning (2008).

Geology from Stearns and Macdonald (1946), Wolfe and Morris (1996), Sherrod and others (2007).

EXPLANATION

)

Age of lava flows

1,500 to 3,000 years

3,000 to 5,000 years

5,000 to 11,000 years

Water-sampling site

Anchialine pool

Dry well (storm drain)

Park boundary

Hydrography

Highway

Road

Tax Map Key boundaries

156° 155°

20°

19°

Area

of

map

Lava

boulders

Coral

reef

Honokōhau

Bay

Island of

Hawai‘i

Kaloko-Honokōhau

National Historical

Park

Figure 3. Map showing locations of water sampling sites and age of lava flows at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i. Also sampled was Honokōhau well, 4.5 mi inland (to the east) at 

1,675 ft above sea level (fig.1). Refer to table 1 for site names, abbreviations, and other related information.
6

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

The study was designed and proposed jointly by the 

National Park Service (NPS) and the U.S. Geological Survey 

(USGS), and was selected and funded under the NPS/USGS 

Water-Quality Partnership Program, that provides hydrologic 

information and understanding needed to preserve natural and 

cultural resources and values of the National Park System.

Environmental Setting and 

Previous Studies

Kaloko-Honokōhau National Historical Park occupies 

coastal lowlands on the flank of Hualālai Volcano, one of 

several major shield volcanoes that have coalesced to form 

the Island of Hawai‘i. The west flank of Hualālai intercepts 

moist oceanic air and causes orographic lifting and condensation, forming a persistent cloudbank part way up the mountain. 

Mean annual precipitation ranges from about 20 in. at the 

coast to more than 79 in. about 2,000 ft above sea level, before 

diminishing to 20 in. or less near the volcano summit above 

7,000 ft (fig. 4). Areas near the coast are generally hot and dry 

in the daytime, with clear to partly cloudy skies. Midslope 

areas beneath the orographic cloudbank are wetter and cooler, 

and extensive suburban bedroom communities have been built 

there to take advantage of the pleasant climate. Groundwater 

recharge is greater in the midslope area as a result of more 

frequent rain showers (Engott, 2011), although there is some 

recharge even in the driest coastal areas during infrequent 

torrential rains. These torrential rains are brought by seasonal 

winter low-pressure and frontal systems, and less frequently 

by hurricanes. Torrential rains tend to blanket the entire area, 

including the normally dry coastal lowlands.

Hualālai is a young and still-active volcano, although 

eruptions are infrequent. Lava flows at the land surface range 

from as old as 30,000 years to the youngest flow in 1800–01 

that spread along the coast where Kona International Airport 

was later built (Wolfe and Morris, 1996). The volcanic rocks 

form a highly permeable aquifer, although with some lowpermeability elements (ash beds, buried soils, intrusive dikes, 

and other structures) that impede groundwater flow. Soils and 

vegetation cover older surfaces of Hualālai Volcano but are 

poorly developed or absent on its youngest surfaces.

Within the Park, three groups of lava flows of varying 

age have been mapped: 1,500–3,000 yr, 3,000–5,000 yr, and 

5,000–11,000 yr (fig. 3). The youngest lavas have a surface of 

blocky or ropy rock on which only a few tufts of grass or other 

plants have taken root (fig. 5A). Intermediate-age lavas have 

somewhat more vegetation, but areas with particularly hummocky, irregular terrain (fig. 5B) have almost as little vegetation as the youngest lavas. The oldest terrain is extensively 

vegetated, although very little soil has developed and vegetation consists mostly of grasses and shrub brush (fig. 5C) 

with some tree groves at low elevations where the water 

table is shallow and coastal sediments are more favorable for 

root development.

Because younger lavas overran and covered older terrain, 

the older lavas occupy low ground locally. Near the coast, this 

low ground is being drowned by island subsidence (Apple 

and Macdonald, 1966), resulting in the two large fishponds 

within the Park. ʻAimakapā Fishpond (fig. 6) would likely be 

a coastal embayment if not for the baymouth barrier berm of 

beach sand built up by waves, separating it from the ocean. 

Lacking a similar sand barrier, Kaloko Fishpond is an embayment that has been closed in by a rock wall built by Native 

Hawaiians.

Groundwater in the area exists as a coastal freshwaterlens system and as inland impounded-groundwater. Previous studies and interpretations have assumed that the 

inland impounded-groundwater and coastal freshwater-lens 

systems are hydrologically connected (Oki and others, 

1999). However, recent information from 2012–14 suggest 

a low-permeability feature confines groundwater beneath 

the coastal lens and forms a coastal confined-groundwater 

system (Tillman and others, 2014). Water in the coastal 

confined-groundwater system is from the inland impoundedgroundwater system. The extent of the hydrologic connection 

between the inland impounded groundwater and freshwaterlens systems is uncertain (fig. 7).

Groundwater in the freshwater-lens system flows from 

inland to the shore with the water table increasing from about 

1 to 5 ft above sea level inland (fig. 7). The lens is actually 

brackish as a result of freshwater mixing with underlying saltwater. Several miles inland, the water table rises tens to hundreds of feet above sea level in an area of “high-level water” 

that is thought to be impounded by intrusive dikes or other 

structures within the volcano (Kauahikaua, 1993; Kauahikaua 

and others, 1998; Oki, 1999). This water is fresh, and numerous wells have been drilled there (fig. 1) to withdraw the highlevel water for public drinking-water supplies.

Within about a mile of the coast no freshwater remains 

within the freshwater-lens system; mixing by tides and other 

forces is complete so that all groundwater is brackish or saline, 

and unsuitable for drinking. Within the Park, the water table 

of the brackish-water lens ranges from <1 to about 2 ft above 

sea level, and the two large fishponds are large expanses of 

low ground that intersect the water table (fig. 8). Similarly, the 

anchialine pools are simply much smaller low points in the 

terrain that also intersect the water table, rather than extensive 

areas such as the fishponds. Water levels in the ponds and 

pools fluctuate with the ocean tides, as water flows in and out 

of the coastal aquifer over the tidal cycle.
Environmental Setting and Previous Studies 7

Figure 4. Map showing mean annual precipitation (Giambelluca and others, 1986) near Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i. Precipitation is greatest midslope beneath a persistent orographic 

cloudbank.

)

)

)

) )

) ) ) )

)

)

)

)

)

Honokōhau well

156° 155°55'

19°45'

19°40'

19°35'

0 1 2 3 4 MILES

0 1 2 KILOMETERS

Kaloko Light

Industrial Park

Kealakehe

Wastewater 

Treatment Plant

Kailua Bay

Quarry

The Shores

at Kohanaiki

Honokōhau

Harbor

Base from U.S. Geological Survey digital data (2004), 1:24,000, UTM Zone 5, NAD83 datum. Aerial imagery circa 2003-2007, (c) DigitalGlobe, Inc. All Rights Reserved.

156° 155°

20°

19°

Area

of map 

Kona

International

Airport

Kailua-Kona

Honokōhau

Bay

Island of

Hawai‘i

Kaloko-Honokōhau

National Historical

Park

Keauhou Bay

NELHA

500

1,000

1,500

750

1,000

1,000

750

500

2,000

1,500

1,000

6,000

4,000

5,000

3,000

2,000

7,000

H u a l āa l a i V o l c a n o

Landfill

EXPLANATION

)

500 millimeters (19.7 inches)

750 millimeters (29.5 inches)

1,000 millimeters (39.4 inches)

1,500 millimeters (59.1 inches)

2,000 millimeters (78.7 inches)

Water-sampling site

Park Boundary

Mean annual precipitation, in millimeters (inches)

Highways

Elevation (contour interval 1,000 feet)
8

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Figure 5 (left). Photographs showing lava flows of 

different ages at Kaloko-Honokōhau National Historical 

Park, Island of Hawai‘i. A, the youngest flow (1,500–

3,000 yr); view is to the northeast from monitoring 

well KAHO 1, with the KAHO Visitor Center at right 

and Kaloko Industrial Park visible as light-colored 

buildings in the distance at left. B, rough, blocky lava of 

intermediate age (3,000–5,000 yr) near anchialine pool 

AP 53H; view is to the northeast, with Kaloko Industrial 

Park on the right. C, the oldest flow (5,000–11,000 yr), 

with little soil but fairly dense grass and brush cover; 

view is to the east from KAHO 3 monitoring well, with 

Kaloko Industrial Park visible in the middle distance. 

Photographs A and B are by Jeff Perreault and Delwyn 

Oki, USGS; photograph C is by Sallie Beavers, NPS.

Figure 6. Oblique aerial photograph of ʻAimakapā 

Fishpond at Kaloko-Honokōhau National Historical Park, 

Island of Hawai‘i. Looking southeast, the pond lies within 

the oldest and lowest terrain that is being drowned by island 

subsidence. Beyond the pond are younger, unvegetated 

lava flows where the Visitor Center and its semi-circular 

parking lot have been constructed. Aerial photograph by 

Brian Powers, Hawaiian Images, used with permission.

A

B

C
Environmental Setting and Previous Studies 9

B

Pacific

Ocean

Land surface

Water table

A

Pacific

Ocean

Land surface

Water table

Figure 7. Conceptual models of interconnection among groundwater bodies at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i (from Tillman and others, 2014).

Figure 8. Schematic cross section showing how fishponds and anchialine pools intersect the water 

table at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i (from Oki and others, 1999).

EXPLANATION

Brackish water

Saltwater

Water table

Volcanic rocks

Beach deposits

General direction of groundwater flow

Vertical scale greatly exaggerated

PACIFIC OCEAN

‘Aimakapā

Fishpond

Anchialine Pool

Land Surface

0 1,000 FEET

0 100 200 METERS

500

Brackish water

Saltwater
10

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Surrounding Developments and WaterQuality Concerns for the Park

A combination of old, new, and proposed urban developments have the potential to influence water quality in the Park. 

Developments adjacent and just upslope from KAHO that have 

been in place for a decade or longer, include Kaloko Light Industrial Park, a rock quarry, and a landfill (figs. 1, 3). Much farther 

upslope and several miles inland to the east are agricultural parcels and residential subdivisions along the Māmalahoa Highway, 

concentrated at elevations between 1,000–2,000 ft (figs. 1, 4). All 

developments upslope from KAHO, including the industrial park 

and residential subdivisions, are currently (2009) using cesspools 

or septic systems, and are not served by the area’s regional sewer 

system. Immediately south of KAHO is Honokōhau Harbor, and 

slightly farther south and southeast is Kealakehe Wastewater 

Treatment Plant (WWTP), a regional collection and treatment 

system serving the urban center of Kailua-Kona and other developments along the coast.

Adjacent to KAHO on its northern boundary is a resort 

development, The Shores at Kohanaiki, for which grading began 

in 2007, and golf-course greens and fairways had just grown in at 

the time of sampling in 2009. The resort produces its own irrigation water by reverse-osmosis desalination of brackish groundwater and has an assortment of wells of several types including 

(1) groundwater withdrawal wells to supply brackish feed water 

for desalination; (2) injection wells to dispose saline water 

resulting from the desalination process back into the aquifer; 

and (3) monitoring wells to measure changes in the hydrologic 

environment. The resort is sewered and connected to the wastewater treatment plant at Kealakehe. In addition to the existing 

developments just described, additional developments have been 

proposed or are under construction in the area surrounding the 

Park (fig. 1), including residential subdivisions, business and light 

industrial parks, and resorts.

Leading water-quality concerns for the Park include 

(1) possible migration of nutrients and contaminants into the Park 

from surrounding areas; (2) changes in salinity that may result 

from climate change or from withdrawal of fresh groundwater 

that would otherwise flow through the Park; and (3) changes in 

salinity or other water qualities that may result from injection of 

saline water resulting from the desalination process or injection of 

other effluents. Besides development immediately adjacent to the 

Park, water quality in KAHO is also expected to be influenced by 

regional groundwater flow from the volcanic uplands that extend 

miles inland to the east, and by overlying suburban and agricultural activities in those uplands. Park water quality could also 

conceivably be influenced by land use north and south of the Park 

along the coast, with contaminants potentially being conveyed to 

the Park by longshore ocean currents.

Constituents potentially migrating into the Park include 

(1) nutrients and other dissolved substances from natural watershed sources (atmospheric deposition, soil fixation, decomposition of forest litter, rock weathering); (2) fertilizer nutrients from 

landscaping and agriculture; (3) urban chemicals from spills, 

improper disposal, or in-roadway runoff; (4) nutrients and chemicals from wastewater sources (cesspools, leaking sewer lines, 

and discharge from the regional wastewater treatment plant at 

Kealakehe); and (5) atmospheric deposition of automotive emissions from vehicular traffic.

Suburban and commercial developments upslope from the 

Park to the east utilize cesspools or septic systems. Wastewater leachate from these sources can be expected to infiltrate to 

the water table and join laterally flowing groundwater that has 

recharged farther upslope. The leachate will contain elevated concentrations of nitrogen and phosphorus, laundry detergents, and 

various personal care products and household cleaning products, 

some of which may contain solvents. Whether these contaminants 

can be detected in groundwater will depend on the sensitivity of 

laboratory methods, the degree of dilution by cleaner groundwater, and the degree of degradation or attenuation of nutrients and 

other constituents in the aquifer. The cesspool and septic seepage 

in the uplands is widespread enough that it can be considered a 

nonpoint source or, alternately, a widespread assortment of many 

small point sources.

At Kealakehe WWTP, municipal wastewater receives secondary treatment in aerated lagoons, is disinfected with chlorine, 

and is disposed to a seepage pit in a permeable lava field inland 

from the treatment plant and across the main highway (Van Dyke, 

2001). From there, the treated effluent joins and displaces ambient groundwater flowing to the coast. Honokōhau Harbor, having 

been excavated into the coast, is thought to preferentially intercept much of the local groundwater discharge from the surrounding land area (Bienfang, 1980; Bowles and others, 2006; Johnson 

and others, 2008). Disposal of treated effluent at Kealakehe has 

averaged about 1.5 Mgal/d (million gallons per day) in recent 

years (Jensen, 2013). This effluent flow is imposed over an 

ambient groundwater flow that has been estimated at 3 Mgal/d 

per coastline mile (Oki and others, 1999). The effluent therefore 

represents a large point source of sufficient volumetric rate that 

it can be expected to largely divert ambient groundwater flow 

around it for some distance, forming a horseshoe-shaped plume 

extending to the coast and embedded in the ambient groundwater 

flow from uplands to the sea (figs. 8–30 of Bear, 1979). Treated 

wastewater effluent discharging to Honokōhau Harbor or along 

the Kealakehe shoreline could conceivably be conveyed northward to marine areas of the Park at times by longshore ocean 

currents; these marine areas include Kaloko Fishpond, which has 

an opening in its seaward rock wall.

Concern has been raised about roadside storm drains called 

“dry wells” (fig. 3) that direct roadway runoff to underlying deep 

aquifers. This stormwater may carry contaminants to groundwater 

and ultimately to receiving waters such as the ponds, anchialine 

pools, and marine waters of the Park. Contaminants could include 

oil and grease, fuel hydrocarbons and products of incomplete 

combustion, nitrogen compounds, and solvents, detergents, and 

other chemicals that might be used or spilled on paved areas and 

later flushed into the roadside drains. Potential contamination 

from dry wells was studied by Izuka and others (2009).

Previous Studies

There have been many notable studies of water and 

biological resources in and near Kaloko-Honokōhau National 

Historical Park. Brock and others (1987) measured water quality in the Park’s anchialine pools and concluded that groundwater was a principal source of nutrients for the pools. Brock 
Sampling Sites, Field Methods, and Laboratory Analysis

11

and Kam (1997) reviewed the biological functioning of the 

Park’s anchialine pools and measured water quality in groundwater, anchialine pools, fishponds, and nearshore marine 

waters at the Park. Brock also conducted a water-quality 

monitoring program for Kohanaiki Golf Club and Resort 

at The Shores at Kohanaiki, the resort development adjoining the Park to the north (Brock, 2010). Dollar and Atkinson 

(1992) had earlier studied nutrient fluxes from similar resort 

golf courses and landscaping at resorts far north and south 

of the Park. Bienfang (2007; 2008) conducted a two-year 

study of nutrient sources, nutrient fluxes, and water quality of 

ʻAimakapā and Kaloko Fishponds, and also reported data for 

anchialine pools and wells in the Park and surrounding region.

The National Park Service has actively accumulated data 

on aquatic and marine resources to establish baseline conditions prior to construction or expansion of various large-scale 

developments. The NPS assessed baseline water-quality 

data (2000) and coastal and watershed conditions at KAHO 

(Hoover and Gold, 2005). The NPS monitors water quality at 

KAHO and other national parks in the Pacific under its NPS 

Inventory and Monitoring Program (HaySmith and others, 

2005). 

Migration of nutrients and contaminants is not uniquely 

a park concern. Statewide, sections of Hawaiian coastal 

waters have been designated as impaired water bodies or 

“Water Quality Limited Segments” for exceeding one or more 

water-quality criteria such as nutrients and suspended sediment. Nutrient-related concentrations (total nitrogen, nitrite 

plus nitrate, total phosphorus, chlorophyll-a, and ammonium) 

in coastal water in the Honokōhau area have exceeded 

water-quality criteria (Hawai‘i State Department of Health, 

2006; 2013).

Bienfang (1980) measured water quality in the adjacent 

Honokōhau Harbor and documented cold, nutrient-rich, brackish groundwater discharging from springs and floating as a 

thin layer on warmer seawater within the harbor. Bienfang and 

Johnson (1980) studied phytoplankton production within the 

harbor and found evidence of sewage contamination from a 

local comfort station. Cold, nutrient-rich, brackish groundwater discharging to the harbor and adjacent coastal margin was 

identified by thermal-infrared imagery and extensive waterquality sampling of ocean waters and wells by Johnson and 

others (2008).

Bowles and others (2006) described geology and groundwater flow directions in the vicinity of the Park, and Bowles 

(2007) offered evidence that the brackish groundwater lens 

in the Kona area is underlain by cold, nutrient-rich saline 

groundwater very different from the warm, nutrient-poor surface seawater just offshore. Bowles hypothesized that the cold 

saline groundwater originates as subthermocline seawater that 

enters the island aquifer at depth offshore, below the warm 

surface-mixed layer.

The USGS has conducted or participated in studies of 

various elements of the Park’s resources. These include an 

inventory of anchialine pools and their fauna (Foote, 2005), a 

benthic marine habitat map of park waters (Gibbs and others, 

2007), geologic resources of the Park (Richmond and others, 

2008), and coastal circulation and submarine groundwater 

discharge along the coast at KAHO (Storlazzi and Presto, 

2005; Presto and others, 2007; Knee and others, 2008; 2010; 

Street and others, 2008; Grossman and others, 2010). USGS 

reports on groundwater resources, including groundwater 

modeling, include Oki (1999) for the general Kona area, and 

Oki and others (1999) for the KAHO park specifically.

In 2002, the USGS analyzed semivolatile organic 

compounds in KAHO groundwater, fishpond sediments, fish 

tissue, and nearshore waters, detecting only a few compounds 

at low, trace-level concentrations below laboratory reporting 

levels. Pentachloroanisole, a degradation product of pentachlorophenol, was detected in the KAHO 2 well (U.S. Geological 

Survey, 2003, written commun.).

South of the Park, Hunt (2008) analyzed nutrients, pharmaceuticals, and wastewater compounds in treated wastewater 

at Kealakehe WWTP and found that two pharmaceuticals in 

the treated effluent were detectable at two coastal springs in 

Honokōhau Harbor and in water from two monitoring wells 

between the Kealakehe wastewater disposal pit and the harbor. 

Similar testing on Maui detected the same pharmaceuticals 

(carbamazepine and sulfamethoxazole) in nearshore coastal 

waters where groundwater effluent plumes of treated, injected 

wastewater emerged at the shore near Kīhei and Lahaina 

(Hunt and Rosa, 2009). Mapping of nitrogen and other 

constituents defined a mile-wide effluent plume at Kīhei, in 

good agreement with model estimates of plume width by Hunt 

(2007). The wastewater injection rate at Kīhei was twice that 

at Kealakehe (3 Mgal/d versus 1.5 Mgal/d), but the ambient 

regional groundwater flow rate was the same in both locales 

(3 Mgal/d per coastline mile).

Sampling Sites, Field Methods, 

and Laboratory Analysis

Two rounds of water sampling were conducted in 2009 to 

establish baseline water-quality conditions at the Park for measured constituents. The first sampling round was conducted 

from July 23–29 (hereafter referred to as the “July” sampling) 

and the second round was from November 30– December 2 

(the “December” sampling).

Sampling Sites

Sampling site descriptions are listed in table 1. With one 

exception, locations of all sampling sites are shown on figure 

3; the location of the Honokōhau well is shown on figures 1 

and 4. Two drinking-water sources were sampled. The first 

was the Honokōhau well, a production well off Māmalahoa 

Highway part way up the mountain flank at an elevation of 

1,675 ft above sea level (fig. 1). This well was sampled at the 

wellhead, before tank storage and water treatment, and the 

sample should provide a good representation of upland “background” freshwater quality because land farther upslope from 
12

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

the site is mainly forest preserve and low-intensity pasture. 

Average pumpage for the period January through September 

2008 was 1.7 Mgal/d. The second drinking-water source was 

tap water at the NPS office at Kaloko Light Industrial Park. 

This water is supplied mainly by the Honokōhau well but may 

contain some water blended in from other wells, most commonly from the Keahuola QLT 1 well (fig. 1). Water from the 

NPS office tap is chlorinated by the distribution system.

Kohanaiki irrigation water was sampled from a lined, 

open-water pond where it is stored before being used to 

irrigate landscaping at the resort. This water is produced by 

reverse-osmosis (RO) desalination of brackish groundwater. 

The pond is exposed to the environment and supports some 

aquatic plant and animal biota, algae being the most obvious 

visually.

Five monitoring wells were sampled, including three NPS 

wells within the Park and two wells at Kohanaiki, along the 

north boundary of the Park. All of the wells except Kohanaiki 

MW401 are short-screened wells with open intervals extending less than 11 ft below sea level. Kohanaiki MW401 is one 

of several deep salinity monitoring wells in the area, extending 131 ft below land surface to 115 ft below sea level. NPS 

measures depth profiles of salinity and temperature in the well 

using a downhole sensor, profiling the brackish groundwater 

lens and saltwater beneath.

Four of the anchialine pools in the Park were sampled. 

AP 016 and AP 53H are only a couple of feet in their largest 

dimension (AP 53H is shown in fig. 2); however, AP 099 and 

AP 144 are somewhat larger, with a width of about 10 ft.

Finally, samples were collected from the two large fishponds within the Park. Kaloko Fishpond was sampled at site 

G18, and ʻAimakapā Fishpond was sampled at site A45. The 

numbered sites are at discernible springs contributing groundwater inflow to the ponds and were located by their latitude 

and longitude coordinates while sampling from a kayak, so as 

to not stir pond-bottom mud into the water samples.

Table 1. Water sampling sites in and around Kaloko-Honokōhau National Historical Park, Island of Hawai‘i, July and 

December 2009.

[USGS, U.S. Geological Survey; NPS, National Park Service; KAHO, Kaloko-Honokōhau; MW, monitoring well; AP, anchialine pool; dip samples were collected 

10 centimeters below water surface; database limitations preclude the use of Hawaiian diacritical marks in USGS station names]

Type of site USGS station name Name used in this 

report

Alternate or 

supplemental NPS 

designation

USGS station ID Sampling 

method

Production well 8-4158-02 Honokohau, 

HI

Honokōhau well Honokōhau well 194056155575201 Hose bib at wellhead

Tap water Kaloko National Park 

Office, HI

NPS tap water KAHO office 194122156011801 Hose bib at NPS 

office

Irrigation water Kohanaiki irrigation 

pond, HI

Irrigation pond Kohanaiki irrigation RO 194131156014801 Dip sample

Monitoring well 8-4061-01 KAHO 

Well 1

KAHO 1 Visitor Center well 194053156013001 Sampling pump

Monitoring well 8-4161-02 KAHO 

Well 2

KAHO 2 Upper Kaloko well 194120156013501 Sampling pump

Monitoring well 8-4161-01 KAHO 

Well 3

KAHO 3 Lower Kaloko well 194125156015501 Sampling pump

Monitoring well Kohanaiki MW400, HI MW400 Kohanaiki makai well 194127156020401 Sampling pump

Monitoring well 8-4161-11 Kohanaiki 

MW401, HI

MW401 Kohanaiki mid well deep 194128156015601 Sampling pump

Anchialine pool Kaloko Anchialine 

Pool 144, HI

AP 144 144 194125156020501 Dip sample

Anchialine pool Kaloko Anchialine 

Pool 53H, HI

AP 53H 053H 194100156015301 Dip sample

Anchialine pool Kaloko Anchilaine 

Pool 016, HI

AP 016 016 194050156014701 Dip sample

Anchialine pool Kaloko Anchialine 

Pool 099, HI

AP 099 099 194014156013301 Dip sample

Fishpond North Kaloko Fishpond 

G18, HI

Kaloko Fishpond 

G18

G18 194122156015901 Dip sample

Fishpond Aimakapa Fishpond 

A45, HI

‘Aimakapā Fishpond 

A45

A45 ‘Aimakapā 194043156013201 Dip sample
Sampling Sites, Field Methods, and Laboratory Analysis

13

Field Methods

Sample Collection

The method of water sample collection varied depending 

on the type of site (table 1). Pressurized sources (Honokōhau 

well and NPS tap water) were sampled by connecting Teflon 

sample tubing to a hose bib. Monitoring wells were sampled 

with a Fultz stainless steel portable sampling pump with 

Teflon riser tubing, pumping at a low rate of 0.5 L/min (liter 

per minute) and allowing a half-hour purging period in which 

water physical properties (temperature, pH, dissolved oxygen, turbidity, and specific conductance) were monitored and 

stabilized in a flow-through chamber. At ponds and pools, 

a dip sample was taken from 10 cm below water surface, 

bottles were uncapped and capped underwater to minimize the 

effect of any surface film that might be present. Samples were 

collected and processed according to USGS protocols (U.S. 

Geological Survey, variously dated), filtered and placed on ice 

in the field, refrigerated overnight at the end of the workday, 

and air-shipped in iced coolers to USGS laboratories.

Laboratory analyses and field measurements made on the 

water samples are listed in table 2. Nutrient samples (nitrite + 

nitrate, ammonia nitrogen, and orthophosphate) were filtered 

into polyethylene bottles pre-rinsed with deionized water and 

field rinsed three times with the filtered sample water (0.45 μm 

[micrometer] filters were used). Unfiltered water samples were 

collected in pre-baked glass bottles to test for pharmaceuticals 

and wastewater compounds; the pharmaceuticals sample was 

later filtered at the USGS National Water Quality Laboratory 

(NWQL) in Denver. Volatile organic compounds (VOCs) were 

collected as unfiltered water in pre-baked glass VOC vials, 

three vials per site. Samples for water isotopes of hydrogen 

and oxygen were collected unfiltered in glass bottles. Samples 

for nitrogen and oxygen isotopes in dissolved nitrate were 

collected in the same manner as nutrient samples, but with 

an added 0.2 μM filter inline after the 0.45 μM filter, and 

were frozen until shipped. Boron and strontium isotopes were 

sampled in the same manner as nutrient samples (filtered water 

collected in polyethylene bottles). A chlorofluorocarbon (CFC) 

water-dating sample was collected at the Honokōhau well by 

routing the sample tubing into an overflowing container, and 

filling and capping glass sample bottles underwater to prevent 

exposure to the atmosphere. Samples were also collected to 

test for optical brighteners (laundry fabric whiteners); these 

were unfiltered water samples collected in 125-mL opaque 

brown polyethylene bottles and chilled in the field.

Quality-Assurance Samples

In addition to the environmental samples, field qualityassurance (QA) samples included one blank for each sampling 

round and one replicate for the December sampling round. 

The blanks and replicate samples were applied selectively 

across analytical methods as a cost-saving consideration. The 

field blanks were prepared by running inorganic blank water 

and nitrogen-purged VOC-free organic blank water through 

the portable sampling pump and tubing after a standard 

decontamination cycle (detergent rinse, tap water rinse, 

methanol rinse, organic blank water rinse). The blank results 

allow one to judge the effectiveness of the decontamination in 

preventing carryover contamination from well to well, and to 

identify possible laboratory artifacts such as detections in both 

environmental samples and field blanks. The portable pump 

was the sampling method most susceptible to carryover contamination, therefore the blanks were applied there rather than 

on the dip-sampling procedure. The July blank was collected 

after sampling KAHO 2 (the first site sampled in July) and its 

subsequent decontamination cycle. The December blank was 

collected after sampling KAHO 3 and its subsequent decontamination cycle, which was performed at KAHO 2 before it 

was sampled. A thorough decontamination cycle also was performed on the sampling pump and tubing at the office before 

equipment was taken into the field in July.

In addition to these field QA samples, USGS laboratories 

conducting their analyses also collect extensive laboratory 

QA samples, including blanks, replicates, and spikes to verify 

the validity of their results and to set method detection and 

reporting levels.

Field Measurements of Water Physical 

Properties

Field measurements of water physical properties were 

made with a multiparameter water-quality sonde (Hydrolab 

DS-5) and included temperature, pH, dissolved oxygen, 

turbidity, and specific conductance, from which salinity 

was computed. All properties were measured in July, but in 

December the multiparameter sonde malfunctioned after the 

first day of use and only specific conductance was measured 

on the remaining days using a handheld conductance meter 

(Yellow Springs Instruments EC-300). Instruments were 

calibrated with standard solutions for specific conductance, 

pH, dissolved oxygen, and turbidity according to manufacturer 

instructions and USGS protocols. Barometric pressure was set 

to the sea-level-adjusted observation from the nearest National 

Weather Service station each morning. Dissolved-oxygen saturation was computed using the DOTABLES online calculator 

(U.S. Geological Survey, 2008) that employs the methodology 

of Weiss (1970).

Computation of Salinity, Saltwater Fraction, 

Freshwater Fraction

Salinity was computed from specific conductance 

(Wagner and others, 2006, equation 9) and saltwater and freshwater fractions in each sample were further computed from 

salinity using values of 35 for seawater and 0 for pure freshwater. Expression of salinity as percent seawater or freshwater 

allows easier understanding for non-specialists who are not 

as conversant with the salinity scale used by oceanographers 

and environmental scientists. Although pure freshwater and 

standard seawater are used as end members rather than actual 

groundwater and seawater in the vicinity, this is an acceptable 
14

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

simplification for comparative purposes in this study, and it 

avoids the inconsistency that arises when actual end members 

differ over time and space.

Laboratory Analysis

Laboratory analyses were conducted by each of the 

USGS laboratories using their standard methods and qualityassurance procedures. Results from the July sampling are 

tabulated in table 3 and those from the December sampling 

are in table 4 (tables 3 and 4 available online at http://dx.doi.

org/10.3133/sir20145158). Concentrations are reported as 

detections (at the numeric value shown), or as non-detections

(“less-than” values with the “<” sign followed by the 

laboratory reporting level). 

The Honokōhau well and NPS office tap water were 

sampled in July only because (1) a one-time characterization 

was expected to capture most of the explanatory value and 

(2) the costs and effort of repeat sampling were considered 

better spent on other environmental samples. At Kohanaiki 

deep monitoring well MW401, two samples were collected 

in “December” (more precisely November 30): one from 5 ft 

below the water surface in the well, and a second sample to 

obtain saltier water by lowering the pump as far as it would go 

(45 ft below the water surface in the well; much less than the 

full well depth of 115 ft below water). 

Recomputation of Reported Nutrient 

Concentrations

Dissolved nutrients (tables 3, 4) were reported by 

the laboratory in milligrams per liter for ammonia (NH3), 

nitrite+nitrate (NO2+NO3), and orthophosphate (PO4). Results 

are stated “as N” and “as P” regardless of the form of speciation. Nitrogen species were summed to compute dissolved 

inorganic nitrogen (DIN=NH3+NO2+NO3). Results are shown 

as reported from the laboratory in milligrams per liter (mg/L; 

also known as parts per million) and recomputed to micrograms per liter (μg/L; also known as parts per billion) and 

micromoles per liter (μM/L, or simply μM, for micromolar) 

because different units are used within different segments of 

the water-quality discipline (terrestrial, marine, and so forth). 

Table 2. Laboratory methods and field measurements for water samples collected at Kaloko-Honokōhau National 

Historical Park, Island of Hawai‘i, July and December 2009.

[USGS, U.S. Geological Survey; N, nitrogen; P, phosphorus; H, hydrogen; O, oxygen; B, boron; Sr, strontium; nm, nanometers; –, not applicable]

Type of analysis or 

measurement USGS method Laboratory or measurement Reference

Nitrogen, nitrite + nitrate, as N Lab code 1979 National Water Quality Lab1 Fishman (1993)

Nitrogen, ammonia, as N Lab code 3116 National Water Quality Lab1 Fishman (1993)

Orthophosphate, as P Lab code 3118 National Water Quality Lab1 Fishman (1993)

Pharmaceuticals (filtered at the 

laboratory)

Schedule 2080 National Water Quality Lab1 Furlong and others (2008)

Wastewater compounds, unfiltered Schedule 4433 National Water Quality Lab1 Zaugg and others (2006)

Volatile organic compounds (VOCs) Schedule 2020 National Water Quality Lab1 Connor and others (1998)

Stable isotopes of H, O in water Schedule 1142 Reston Stable Isotope Lab2 Révész and Coplen (2008a, 2008b)

Stable isotopes of N, O in dissolved 

nitrate

Schedule 2900 Reston Stable Isotope Lab2 Révész and Casciotti (2007a, 2007b)

Stable isotopes of B, Sr in water – Menlo Park Stable Isotope Lab3 –

Chlorofluorocarbon (CFC) recharge 

date

– Reston Chlorofluorocarbon Lab4 –

Specific conductance, temperature, 

pH, dissolved oxygen, turbidity

– Multiparameter sonde U.S. Geological Survey (variously 

dated)

Specific conductance – Handheld meter U.S. Geological Survey (variously 

dated)

UV fluorescence at 445 nm emission

 wavelength (optical brighteners)

– Handheld meter Turner Designs (2004)

1

USGS National Water Quality Laboratory, Denver, Colo.

2

USGS Reston Stable Isotope Laboratory, Reston, Va.

3

Thomas D. Bullen, Branch of Regional Research, Menlo Park, Calif.

4

USGS Reston Chlorofluorocarbon Laboratory, Reston, Va.
Sampling Sites, Field Methods, and Laboratory Analysis

15

Hawai‘i water-quality standards are expressed primarily in 

micrograms per liter (Hawai‘i State Department of Health, 

2006; 2013). The dominant fraction of DIN in all samples was 

nitrite-plus-nitrate, within which nitrate is generally the dominant dissolved species in natural waters (Hem, 1985).

Low-Level Detections

For the organic compounds (pharmaceuticals, wastewater 

compounds, volatile organic compounds), most results were 

non-detections. Bold and shaded values in the tables are highconfidence detections having 99 percent or greater confidence 

that they are not false positives. Other reported detections in 

plain text are lower in confidence and may not represent true 

environmental detections. Some are very low “trace-level” 

concentrations with greater than a 1 percent chance of being 

false positives (see footnote 1). Others correspond to detections in field or laboratory blanks at similar concentrations, 

raising the prospect that they are artifacts of sampling or 

laboratory contamination (see footnote 2). Results are reported 

in micrograms per liter (μg/L), also known as parts per billion. 

Values in decimal fractions less than one are “sub-parts-perbillion” concentrations, also known as parts-per-trillion.

Detections designated with the prefix “E” for estimated 

are mostly very low concentrations below laboratory reporting levels—commonly referred to as “trace” by other laboratories. Methods in use by the USGS National Water Quality 

Laboratory (NWQL) for these compounds use a combination 

of chromatography and mass-spectrometry for compound 

identification and quantitation (referred to as information-rich 

methods that are discussed more in the following paragraph). 

E-coded values are lower than the laboratory reporting level 

(LRL) and lowest calibration standard used in the method. 

The concentration is flagged as estimated because its numeric 

value is subject to more uncertainty than concentrations within 

the calibration range, as bracketed by prepared calibration 

standards. However, the compound is judged to be present 

by agreement between the chromatograph peak and mass 

spectrometer ionic fragments matching the same compound. 

Concentrations below the LRL also run an increased chance 

of resulting in false negatives (constituent is present but not 

reported) and detection and reporting might vary from sample 

to sample or from day to day in the laboratory (Childress and 

others, 1999). Finally, results that exceed the highest calibration standard also are flagged with the E code.

Of similar relevance is the Long-Term Method Detection 

Level (LT-MDL), which is one-half the LRL and is set so that 

there is a greater than 99 percent probability that the reported 

concentration is not a false positive (constituent reported 

but not actually present). Quoting from Childress and others 

(1999): 

At the LT–MDL concentration, the chance of a false 

positive detection is statistically limited to <1 percent. 

At concentrations less than the LT–MDL, the risk of 

false positive detections can increase rapidly. Mass 

spectrometric or photodiode array ultraviolet/visible 

spectroscopic detectors used for organic methods 

are classified by the NWQL as “information-rich” 

methods because they have enhanced analyte identification capabilities. For these methods, the NWQL 

will report values below the LT–MDL, along with an 

estimated “E” remark code, because the criteria for 

identification must be met before quantitative results 

are reported ... Although information-rich methods 

provide enhanced analyte identification capabilities, 

concentrations reported below the LT–MDL still 

have an increased risk (>1 percent) of being a 

false positive.

The LRL and LT-MDL are set by statistical analysis of 

large numbers of laboratory blanks and spikes. To summarize, 

the LRL is set high enough to give 99 percent assurance 

against false negatives (constituent present but not reported) 

and the LT-MDL is set low enough to give 99 percent assurance against false positives (constituent reported but not actually present). For a more thorough discussion see Childress 

and others (1999).

M-flagged entries indicate that a constituent is present but 

that no estimate of concentration is made. For this study, the 

M code is only used for the “sniff test” for hydrogen sulfide. 

Very low concentrations of hydrogen sulfide can be detected 

by smell, but in this case no chemical analysis was performed 

to determine the concentration. Hydrogen sulfide was smelled 

in only one sample, the July sample from KAHO 1, the monitoring well at the NPS Visitor Center (table 3).

Stable Isotopes and Isotope Notation

Under favorable conditions, stable isotopes can be used 

to infer the origin and modification of water and nutrients. 

Isotopes are variant atomic forms of an element in which the 

atomic nucleus has the same number of protons but differing numbers of neutrons. Isotopic compositions measured in 

this study include δ15N and δ18O of dissolved nitrate (NO3), 

δ2H and δ18O of water (H2O), δ11B of dissolved boron, and 

the 87Sr/86Sr ratio of dissolved strontium. The various isotopic 

measures are ratios of a heavier isotope to a lighter isotope for 

a given element (15N to 14N, 18O to 16O, 2H to 1H, 11B to 10B, 87Sr 

to 86Sr). The δ symbol signifies “delta notation” and is read as 

“delta-N-15,” “delta-O-18,” “delta-H-2,” and “delta-B-11.” 

Units are parts per thousand (per mil, denoted by the ‰ symbol) and normalized to reference standards: atmospheric air 

(AIR) for N, Vienna Standard Mean Ocean Water (VSMOW) 

for O and H, and National Bureau of Standards (NBS) 951 

for B. Isotopic compositions can be positive or negative, with 

larger or more positive values referred to as “heavier” and 

smaller or more negative values as “lighter.” Positive and 

negative values arise from a sample being isotopically heavier 

or lighter than the reference standard to which it is being compared. Further explanation can be found in texts on isotope 

chemistry, for example Kendall and McDonnell (1998).
16

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Hydrogen and oxygen isotopes in water (δ2H and δ18O) 

characterize the water molecule, H2O. Isotopic fractionation in 

water is a partitioning process whereby isotopic composition 

is changed mainly during phase changes: during condensation 

from water vapor or evaporation from liquid water back to 

vapor. These processes occur in clouds where water precipitates, on the landscape where some fraction of precipitation 

evaporates, and by evaporation from standing water (lakes, 

streams, marshes, and oceans). A useful property of water 

isotopes is that once water infiltrates to the water table, δ2H 

and δ18O tend to remain fixed and behave conservatively (not 

changing, other than by simple mixing) during groundwater 

transport to destinations farther along the flow system. This 

makes them good tracers for some waters, although mixing 

calculations may be needed to correctly interpret the data. 

Groundwater recharged at different elevations in Hawai‘i, 

obtains distinctive isotopic compositions (Scholl and others, 

1995; 2002) that contrast strongly with isotopic compositions 

of seawater.

Nitrogen and oxygen isotopes in dissolved nitrate (δ15N 

and δ18O) may allow the predominant source of the nitrate 

to be inferred under favorable conditions. One such source 

classification, shown in figure 9, was compiled by Kendall 

and McDonnell (1998) from various studies and represents 

results of hundreds of samples. This classification scheme 

has been used to differentiate human and animal waste nitrate 

from nitrate originating throughout the watershed from other 

sources such as plant-fixed soil nitrate or mineral nitrate fertilizers. The range for soil nitrogen (fixed from the atmosphere 

by plants) is centered at roughly δ15N = +5 per mil and δ18O = 

+5 per mil and spans a δ15N range from about +2 to +8 per mil. 

Graphed values for ammonium in fertilizer and rain plot to the 

left: lighter in δ15N but not much different in δ18O. Graphed 

values for nitrate from fertilizer plot up and to the left of those 

for soil nitrate, the fertilizer being heavier in δ18O and lighter 

in δ15N. Manure and septic waste have a broad range spanning 

δ15N = 0 to +25 and centered at δ18O = +5. Finally, graphed 

values for nitrate in precipitation plot at upper left, being 

generally light in δ15N and very heavy in δ18O. The actual 

amount of nitrate in precipitation is small, however, so the 

isotopic composition of most groundwater will be dominated 

by the terrestrial sources of nitrate plotted along the bottom of 

the graph.

Compositions anywhere on the plot can be modified 

by fractionation processes in which a physical, chemical, or 

biologic process selectively incorporates the lighter or heavier 

isotope and leaves behind a residual pool of material enriched 

in the other isotope. The large arrow shows a denitrification 

trend at a slope of 1:2, or 1 unit change in δ18O for every 2 

units in δ15N. Denitrification of nitrate to N2 gas is one of a 

number of microbial nitrogen-cycling processes carried out by 

bacteria that cause isotopic fractionation, in this case driving 

isotopic values heavier while reducing nitrate concentration. 

The processes include volatilization of ammonia, nitrification of ammonium to nitrate, denitrification, and anammox 

(anaerobic oxidation of ammonium to N2 gas). Biologic 

uptake or assimilation of nitrate by phytoplankton also drives 

isotopic values heavier, but at a steeper slope of 1:1 (Granger 

and others, 2004). This trend was not shown on Kendall and 

McDonnell’s classification (fig. 9) but is shown on figures 

later in the report because biologic uptake is likely an active 

process affecting the fishponds and anchialine pools at KAHO.

Optical Brighteners

Samples were screened by ultraviolet (UV) fluorescence 

as a test for fabric whiteners or “optical brighteners” (table 5). 

These are additives in laundry detergents that act as whitening 

agents, and they impart high fluorescence levels to laundry 

graywater and household wastewater. Fluorescence measurements on environmental water samples can, therefore, be an 

effective screening test for the presence of wastewater and 

(or) graywater (Hagedorn and others, 2005; Hartel and others, 

2007; Cao and others, 2009).

UV fluorescence was measured at the USGS Honolulu 

office using a handheld Aquaflor fluorometer sensing an emission wavelength of 445 nanometers in response to excitation at 

350 nanometers (Turner Designs, 2004; 2007a). All readings 

were made with the instrument at factory calibration setting 

and not re-calibrated to secondary standards. As a result, meter 

readings are in arbitrary fluorescence units and are strictly 

comparable only within the dataset and relative to control 

samples of deionized and tap water. Some environmental readings were negative, but not as negative as the control samples, 

indicating “more fluorescence” than the controls.

Figure 9. Graph showing nitrate source classification 

based on nitrogen and oxygen stable-isotope 

compositions of dissolved nitrate (Carol Kendall, USGS, 

written commun., 2006, her modification from Kendall 

and McDonnell, 1998). Although useful as a general 

guide, compositions can be shifted by fractionation 

processes such as denitrification. NO3, nitrate; NH4, 

ammonium ion; VSMOW, Vienna Standard Mean 

Ocean Water; AIR, atmospheric air.

-10

0

10

20

30

40

50

60

70

80

90

100

-15 -10 -5 0 5 10 15 20 25 30 35 40

manure & septic 

waste

NO3 in

precipitation

 NO3 fertilizer

soil N

microbialnitrification

denitrification

δ15N in dissolved nitrate, in per mil AIR

δ

18O in dissolved nitrate, in per mil VSMOW

NH4 in

fertilizer

and rain
Sampling Sites, Field Methods, and Laboratory Analysis

17

Table 5. Tests for optical brighteners in water samples collected at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i, July and December 2009.—Continued.[Meter readings of UV (ultraviolet) fluorescence at 445 nanometer emission wavelength on a Turner Designs Aquafluor handheld fluorometer with optical brightener channel (excitation UV-375 nm, emission 445 nm) at factory-calibrated settings; samples were read initially and then subjected to illumination from a strong UV lamp for 5 and 10 minutes and re-read each time; results indicating presence of brighteners are bold and shaded; control samples were measured at start and end of the measurement sequence; –, not applicable]

Site Initial UV reading

UV-5 

(reading after 

5 minutes 

illumination)

UV-10 

(reading after 

10 minutes 

illumination)

Test 1a Test 2b

Initial 

minus 

UV-5

Percent-5 

(percent 

reduction at 

5 minutes)

Optical 

brighteners 

present?

Initial 

minus 

UV-10

Percent-10 

(percent 

reduction at 

10 minutes)

Percent-10 

divided by 

Percent-5

Optical 

brighteners 

present?

July samples

Honokōhau 

well

–0.793 –0.432 –1.001 –0.36 –45.5 No 0.208 26.2 –0.58 ––

NPS tap 

water

–1.376 –1.306 –1.393 –0.07 –5.1 No 0.017 1.2 –0.24 ––

KAHO 1 –0.586 –0.692 –0.692 0.11 18.1 Go to test 2 0.106 18.1 1.00 YesKAHO 2 1.463 1.279 1.226 0.18 12.6 Go to test 2 0.237 16.2 1.29 YesKAHO 2 

blank

–1.739 –1.789 –1.890 0.05 2.9 No 0.151 8.7 3.00 ––

KAHO 3 0.152 –0.011 –0.069 0.16 107 Yes 0.221 145 1.36 ––Kaloko 

Fishpond G18

–0.396 –0.405 –0.734 0.01 2.3 No 0.338 85.4 37.13 ––

‘Aimakapā 

Fishpond A45

4.510 4.074 3.872 0.44 9.7 Go to test 2 0.638 14.1 1.45 Yes

Irrigation 

pond

–0.757 –0.911 –0.892 0.15 20.3 Go to test 2 0.135 17.8 0.88 Yes

Kohanaiki 

MW401 shallow

3.264 2.854 2.745 0.41 12.6 Go to test 2 0.519 15.9 1.26 Yes

Kohanaiki 

MW400

–0.570 –0.673 –0.819 0.10 18.1 Go to test 2 0.249 43.7 2.41 No

Anchialine 

Pool 144

2.254 1.917 1.722 0.34 15.0 Go to test 2 0.532 23.6 1.57 No

Anchialine 

Pool 53H

–0.079 –0.099 –0.135 0.02 25.3 Go to test 2 0.056 70.9 2.80 No

Anchialine 

Pool 016

–0.228 –0.387 –0.472 0.16 69.7 Yes 0.244 107 1.54 ––

Anchialine 

Pool 099

2.757 2.543 2.276 0.21 7.8 No 0.481 17.4 2.23 ––
18

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau Table 5. Tests for optical brighteners in water samples collected at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i, July and December 2009.—Continued. [Meter readings of UV (ultraviolet) fluorescence at 445 nanometer emission wavelength on a Turner Designs Aquafluor handheld fluorometer with optical brightener channel (excitation UV-375 nm, emission 445 nm) at factory-calibrated settings; samples were read initially and then subjected to illumination from a strong UV lamp for 5 and 10 minutes and re-read each time; results indicating presence of brighteners are bold and shaded; control samples were measured at start and end of the measurement sequence; –, not applicable] Site Initial UV reading UV-5 (reading after 5 minutes illumination) UV-10 (reading after 10 minutes illumination) Test 1a Test 2b Initial minus UV-5 Percent-5 (percent reduction at 5 minutes) Optical brighteners present? Initial minus UV-10 Percent-10 (percent reduction at 10 minutes) Percent-10 divided by Percent-5 Optical brighteners present? December samples KAHO 1 1.175 0.997 0.959 0.18 15.1 Go to test 2 0.216 18.4 1.22 Yes KAHO 1 replicate 1.498 1.301 1.393 0.20 13.2 Go to test 2 0.105 7.0 0.53 Yes KAHO 1 blank –1.476 –1.412 –1.465 –0.06 –4.3 No –0.011 –0.7 0.16 –– KAHO 2 1.171 1.009 0.876 0.16 13.8 Go to test 2 0.295 25.2 1.83 No KAHO 3 –0.219 –0.312 –0.277 0.09 42.5 Yes 0.058 26.5 0.62 –– Kaloko Fishpond G18 0.616 0.551 0.507 0.07 10.6 Go to test 2 0.109 17.7 1.67 No ‘Aimakapā Fishpond A45 2.922 2.884 2.570 0.04 1.3 No 0.352 12.0 9.23 –– Irrigation pond –0.886 –0.901 –0.945 0.02 1.7 No 0.059 6.7 3.94 –– Kohanaiki MW401 shallow 4.902 4.811 4.528 0.09 1.9 No 0.374 7.6 4.00 –– Kohanaiki MW401 deep –1.474 –1.522 –1.558 0.05 3.3 No 0.084 5.7 1.73 –– Kohanaiki MW400 3.126 2.921 2.855 0.21 6.6 No 0.271 8.7 1.32 –– Anchialine Pool 144 0.891 0.679 0.648 0.21 23.8 Go to test 2 0.243 27.3 1.15 Yes Anchialine Pool 53H 0.733 0.638 0.647 0.10 13.0 Go to test 2 0.086 11.7 0.90 Yes
Sampling Sites, Field Methods, and Laboratory Analysis

19

Table 5. Tests for optical brighteners in water samples collected at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i, July and December 2009.—Continued.[Meter readings of UV (ultraviolet) fluorescence at 445 nanometer emission wavelength on a Turner Designs Aquafluor handheld fluorometer with optical brightener channel (excitation UV-375 nm, emission 445 nm) at factory-calibrated settings; samples were read initially and then subjected to illumination from a strong UV lamp for 5 and 10 minutes and re-read each time; results indicating presence of brighteners are bold and shaded; control samples were measured at start and end of the measurement sequence; –, not applicable]

Site Initial UV reading

UV-5 

(reading after 

5 minutes 

illumination)

UV-10 

(reading after 

10 minutes 

illumination)

Test 1a Test 2b

Initial 

minus 

UV-5

Percent-5 

(percent 

reduction at 

5 minutes)

Optical 

brighteners 

present?

Initial 

minus 

UV-10

Percent-10 

(percent 

reduction at 

10 minutes)

Percent-10 

divided by 

Percent-5

Optical 

brighteners 

present?

December samples—Continued

Anchialine 

Pool 016

0.076 –0.020 –0.023 0.10 126 Yes 0.099 130 1.03 ––

Anchialine 

Pool 099

5.475 5.037 4.814 0.44 8.0 Go to test 2 0.661 12.1 1.51 No

Control samples

Tap water 1 –1.257 –1.298 –1.325 0.04 3.3 No 0.068 5.4 1.64 ––Deionized 

water 1

–1.182 –1.160 –1.190 –0.02 –1.9 No 0.008 0.7 –0.37 ––

Tap water 2 –1.483 –1.580 –1.618 0.10 6.5 No 0.135 9.1 1.40 ––Deionized 

water 2

–1.305 –1.183 –1.408 –0.12 –9.3 No 0.103 7.9 –0.85 ––

Description of test rules for determining presence of optical brighteners (OB) by ultraviolet (UV) illumination (Cao and others, 2009)

aTest 1: If the reduction in fluorescence after 5 min of UV exposure is greater than or equal to 30 percent, the sample contains OB. If the reduction in fluorescence after 5 min of UV exposure is less than 8 percent, the sample does not contain OB. If the reduction in fluourescence is between 8 percent and 30 percent, proceed to Test 2.bTest 2: If the ratio of reduction after 10 min:5 min of UV exposure is less than 1.5, the sample contains OB. If the ratio of reduction after 10 min:5 min of UV exposure is greater than or equal to 1.5, the sample 

does not contain OB.
20

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Fluorescence readings were taken initially, then again 

after 5 and 10 min of illumination by a strong UV lamp, following the testing procedure of Cao and others (2009). This 

procedure takes advantage of the fact that the fluorescence 

response of optical brighteners is more stable than that of 

dissolved organic matter (DOM), which breaks down preferentially under intense UV exposure. The initial, 5- and 10-min 

readings are subjected to empirical formulas to determine if 

optical brighteners are present (Cao and others, 2009).

Hydrologic and Tidal Conditions During 

Sampling

One goal of the study was to sample during both fairand wet-weather to see if groundwater quality differed under 

varied hydrologic conditions. The project proposal stated, 

“The wet-weather sampling will occur within 48 hours of 

heavy coastal rainfall defined as 1.5 inches over 24 hours 

based on data from the park’s Remote Automated Weather 

Station (RAWS)” (Beavers and Hunt, 2008). However there 

were no rains of this magnitude in the year available for field 

work (2009) and both sampling rounds were essentially fairweather samplings conducted during extended periods of hot, 

dry weather.

Daily precipitation records at the KAHO RAWS station 

(fig. 10) indicate that the year 2009 was quite dry compared 

to 2007 and 2008, which had several large daily rainstorms 

respectively. Large precipitation events in 2007 included 

4.37 in. on February 1, 2.23 in. on December 3, 5.02 in. on 

December 5, and 0.85 in. on December 10. In 2008, large 

daily events included 1.93 in. on June 12 and 2.39 in. on 

December 11. In 2009 the site received 0.85 in. on January 11, 

but the gage apparently malfunctioned from around March to 

the end of the year (it could have been partly malfunctioning 

earlier, it is difficult to know).

Figure 10. Graph showing daily precipitation at Kaloko-Honokōhau Park, Island of Hawai‘i, 2007–09 

(Western Regional Climate Center, 2010a). Following heavy December 2007 rains that caused 

groundwater recharge in the Park, 2009 was a dry year, although instrument malfunction for much 

of the year requires that conclusion to be drawn from the nearby Honokōhau Harbor weather station 

observations (fig. 11).

0 

1 

2 

3 

4 

5 

6 

Daily precipitation at Kaloko-Honokōhau Park, in inches 

Kaloko-Honokōhau, Hawai‘i, Station 496017, elevation 25 feet

National Weather Service Remote Automated Weather Station (RAWS) Network,

operated by National Park Service 

July 23–28 sampling

Nov. 30–Dec. 2 sampling

Rain gage malfunctioning

O N D J F M A M J J A S O N D J F M A M J J A S O N D

2008 2009

J F M A M J J A S

2007
Sampling Sites, Field Methods, and Laboratory Analysis

21

The December 2007 rains caused substantial flooding 

in the Kona watershed and runoff plumes of muddy water 

extended offshore in the ocean, witnessed by the author when 

flying in for another sampling project. The December 5, 2007, 

rain of 5.02 in. at the KAHO rain gage was large enough to 

cause groundwater recharge at the Park, discernible as a small 

peak in recorded groundwater levels at KAHO 3 after filtering 

out tidal fluctuations (Delwyn Oki, USGS, written commun., 

2010). The recharge pulse was detected within hours of the 

heaviest hourly precipitation on December 5. This is not 

entirely surprising because the land surface at KAHO 3 is only 

23 ft above mean sea level and the terrain is rough, permeable 

lava with discontinuous soil and only sparse, grassy vegetation. Daily rains less than one or two inches may not generate much recharge in the coastal lowlands, although locally 

focused recharge is possible where runoff is channeled to 

roadside swales, drains, and dry wells.

Given the malfunction at the KAHO RAWS station for 

much of 2009, it is fortunate that precipitation records also 

were available from the nearby Honokōhau Harbor rain gage. 

Monthly precipitation for the years 2000–09, including the 

2009 period of missing data at the KAHO station are shown 

in figure 11. The Honokōhau Harbor records reemphasize the 

magnitude of the December 2007 rains and show 2009 to have 

been a dry year; 2008 was wetter mid-year than is apparent on the daily graph for KAHO (fig. 10). December 2007 

precipitation at the Honokōhau Harbor station was 10.33 in., 

quite similar to the December 2007 total of 9.00 in. at the 

KAHO station.

In summary, heavy rains in December 2007 recharged the 

brackish groundwater lens in the Park and surrounding coastal 

Calendar year

0 

2 

4 

6 

8 

10 

12 

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 

Monthly precipitation at Honokōhau Harbor, in inches 

Honokōhau Harbor, Hawai‘i, Station 511880-6, elevation 30 feet

National Weather Service Cooperative Network 

July 23–28 sampling

Nov. 30–Dec. 2 sampling

Figure 11. Graph showing monthly precipitation at Honokōhau Harbor, Island of Hawai‘i, 

2000–09 (Western Regional Climate Center, 2010b). These data show 2009 was a dry year 

and December 2007 had the largest monthly precipitation total of the decade.
22

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

lowlands, temporarily raising groundwater levels and increasing coastal discharge of groundwater. There may have been 

some lowland recharge in 2008 as well; however, there probably was little to no recharge locally in 2009 in the lowlands 

where KAHO is situated and where most of the sampling was 

conducted. Viewed in this light, both the July and December 

2009 samplings reflect dry-season groundwater conditions if 

the groundwater system had fully recessed from the late 2007 

recharge (that is, if groundwater levels and coastal discharge 

had diminished to baseline levels). Alternately, if the groundwater system was still in recession from late 2007 recharge, 

the July 2009 samples may reflect slightly more of a “wetseason signature” and the December 2009 samples more of 

a “dry-season signature” – being that December would have 

been farther out on the recession than July. If this is true, the 

July 2009 samples may have better captured contaminants 

leached into groundwater through the land surface or by 

way of roadside dry wells during the late 2007 recharge. 

By December 2009, more time had elapsed, possibly allowing greater degradation and sorption of contaminants within 

the aquifer.

Tides and longer-term fluctuations in ocean level have the 

potential to influence sampling results because the brackish 

coastal groundwater lens rises and falls with changes in ocean 

level. Locally, irregular flushing or forcing of water through 

preferential voids and permeable layers in the aquifer likely 

is also occurring. Long-term fluctuations of daily mean ocean 

level for 2009 at the Kawaihae tide gage (National Oceanic 

and Atmospheric Administration, 2010) and groundwater levels in two monitoring wells at the Park, KAHO 2 and KAHO 3 

(U.S. Geological Survey water-level records) are shown in 

figure 12. The Kawaihae tide gage is 26.5 mi north-northeast 

of KAHO. The well water levels closely mimic ocean fluctuations as the groundwater lens rises and falls with changes in 

ocean level. Well water levels were about 0.3–0.35 ft higher 

at the start of July sampling than at the start of December 

sampling. Any effect this slight difference in groundwater 

levels may have had on water quality cannot readily be determined. Although this slight difference may have caused some 

corresponding salinity change in wells and anchialine pools, 

daily tides cause more extreme groundwater fluctuations, and 

some hydrologic evolution in the brackish lens would also be 

expected over the several months between sampling.

-0.5 

0.0 

0.5 

1.0 

1.5 

2.0 

Daily mean water level, in feet above mean sea level 

2009

KAHO 2 water level

KAHO 3 water level

Ocean level at Kawaihae tide gage 

July 23–28 sampling

Nov. 30–Dec. 2 sampling

EXPLANATION

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Figure 12. Graph showing daily mean water levels at Kawaihae tide gage and in monitoring wells 

KAHO 2 and KAHO 3 at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i (National 

Oceanic and Atmospheric Administration, 2010; U.S. Geological Survey water-level records). Wellwater levels closely mimic ocean fluctuations and were about 0.3–0.35 ft higher at the start of July 

sampling than at the start of December sampling.
Sampling Sites, Field Methods, and Laboratory Analysis

23

Water samples could not be collected at a consistent 

stage in the daily tidal cycle because of limitations of completing sampling during daylight hours. Tidal variations during 

sampling are shown in figures 13 and 14, with sample collection times superposed. In these graphs, the sample symbols 

don’t correspond to the measured water levels at the sites; 

they are simply plotted directly on the tidal trend line by 

sample time alone. Tidal time differences between predicted 

tides at Kawaihae and Kailua-Kona (National Oceanic and 

Atmospheric Administration, [2014]) range from several 

minutes to about a half-hour and can be disregarded to a 

first approximation.

Tidal range was more extreme during July sample collection than during December sample collection. In July (fig. 13), 

water samples were collected over a maximum tidal range of 

2.65 ft early in the sampling period when daytime sampling 

hours coincided with the extreme hydrographic limb of the 

daily tide. That range lessened to about 0.6 ft by the end of 

the sampling period as the tides progressed and daytime hours 

fell on lesser hydrographic limbs of the tide. The timing of 

the July sampling, unfortunately, was governed by logistical 

arrangements and could not be shifted to a more favorable 

week in the monthly tidal cycle. The December sampling 

(fig. 14) did take place under a more favorable tidal stage: daytime hours coincided with the lesser limbs of the tidal cycle, 

and all samples were collected within a tidal range of about 

0.8 ft and at fairly low tidal stage overall.

Water-quality results for any site could be somewhat 

dependent on the stage of tide on which the sample was collected. However, there is no way to determine the possible 

effect of this without round-the-clock subsampling at close 

time intervals (for example, hourly or every other hour) at 

each site. This would be an interesting approach for a detailed 

process-level study but is not possible in a reconnaissancelevel study such as this one.

Honokōhau 

well 

NPS

tap water

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko

fishpond

G18 

‘Aimakapā

fishpond 

A45 

Irrigation

pond 

MW401

shallow 

MW400 

AP 144 

AP 53H 

AP 016

AP 099 

KAHO 2 blank 

-1.0 

-0.5 

0.0 

0.5 

1.0 

1.5 

2.0 

23 24 25 26 27 28 29

6-minute ocean level at Kawaihae tide gage, in feet above mean sea level 

July 2009

Ocean level at Kawaihae tide gage

Water sample, plotted by time of sample 

EXPLANATION

Figure 13. Graph showing July 2009 sample collection times at Kaloko-Honokōhau National 

Historical Park in relation to daily tides at Kawaihae tide gage (National Oceanic and Atmospheric 

Administration, 2010), Island of Hawai‘i. Tidal range was extreme during daytime sampling hours 

early in the sampling period but lessened by the end of sampling.
24

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Results and Interpretation

The collected water-quality data are interpreted here 

with several questions in mind: (1) Were notable contaminants found, such as pesticides or solvents? (2) Were naturally 

occurring constituents such as nitrate or phosphorus abnormally high at some sites, high enough to implicate human 

enrichment by fertilizer or septic waste? (3) How similar or 

different were results from the two sampling rounds?

Nutrients, stable isotopes, and selected field measurements are interpreted mainly through the use of X-Y graphs. A 

principal reason for this is that the samples encompass a wide 

range in salinity resulting from mixing of fresh and saline 

source waters. Because the degree of mixing or dilution varies 

from sample to sample along with sample salinity, constituent concentrations are not strictly comparable by their raw 

numeric values alone but are better interpreted in relation to a 

hypothetical freshwater-saltwater mixing line on various plots.

Organic compounds (pharmaceuticals, wastewater 

compounds, and volatile organic compounds) and optical 

brighteners are interpreted mainly by examining their numeric 

values in the respective data tables (tables 3, 4). Although 

these concentrations (or values) may vary somewhat with 

the degree of freshwater-saltwater mixing, a simple mixing 

relationship is not expected and one is limited mainly to discerning whether compounds are detected at all and one is only 

secondarily able to compare concentrations.

Salinity and Temperature

The salinity and temperature of water samples indicate 

that most samples were plausible mixtures of fresh groundwater originating farther inland and colder saline groundwater 

that underlies the coastal brackish groundwater lens. Some 

samples were warmer than would be expected by simple mixing, most likely as a result of solar warming of exposed ponds 

and water transmitted in pipelines under hot roadways.

The relation of temperature versus salinity for July and 

December is shown in figures 15 and 16, respectively. All July 

samples are represented on the plots but the multiparameter 

Figure 14. Graph showing December 2009 sample collection times at Kaloko-Honokōhau 

National Historical Park in relation to daily tides at Kawaihae tide gage (National Oceanic and 

Atmospheric Administration, 2010), Island of Hawai‘i. A favorable relation of tides to daytime 

sampling hours allowed all samples to be collected over a small tidal range and at low tidal stage.

men14-5078_fig14

KAHO 1 

KAHO 1

replicate 

KAHO 2 

KAHO 3 

Kaloko

fishpond

G18 

‘Aimakapā

fishpond A45 

Irrigation

pond 

MW401

shallow 

MW401

deep 

MW400 

AP 144 

AP 53H 

AP 016 

AP 099 

KAHO 1

blank 

-1.5 

-1.0 

-0.5 

0.0 

0.5 

1.0 

1.5 

2.0 

November 30 December 1 December 2 December 3

6-minute ocean level at Kawaihae tide gage, in feet above mean sea level 

2009

Ocean level at Kawaihae

tide gage

Water sample, plotted

by time of sample 

EXPLANATION
Results and Interpretation 25

instrument malfunctioned in December and prevented field 

temperature measurement on all but the first day’s samples 

at the two Kohanaiki monitoring wells (although specific 

conductance was later measured and salinities computed for 

all of the December samples). Most samples had salinities that 

were <50 percent seawater, but a sample from deep monitoring well MW401 was 67 percent seawater and had the lowest 

temperature, reinforcing an earlier finding by Bowles (2007) 

that the brackish-water lens in the Kona area is underlain by 

cold saltwater.

A hypothetical mixing line is drawn in figures 15 and 16 

to represent mixing between upland fresh groundwater and 

deep saline groundwater. Termed the “upland-deep saline 

groundwater mixing line” in this report, it is drawn through 

the July value for the Honokōhau well and the December 

value for the MW401 deep sample. These are the freshest and 

saltiest waters sampled and are, therefore, chosen to represent end members in the hypothetical mixing relation. The 

Honokōhau well is the farthest inland sample and represents 

upland “background” freshwater before additional salts are 

added farther downgradient by tidal mixing and evaporative concentration in low-elevation recharge. Anthropogenic 

constituents also are presumed to be lesser in concentration in 

upland groundwater and to increase downslope with additions from agricultural, suburban, and commercial/industrial 

land activities. The MW401 December sample from 45 ft 

below the water table was the saltiest water collected, having 

a salinity two-thirds that of seawater (a salinity of 23.6, equal 

to 67 percent seawater). If upland groundwater resembling 

that from the Honokōhau well flows toward shore and mixes 

with saline groundwater from which the MW401 deep sample 

originates, then varying mixtures of the waters would fall 

along the hypothetical mixing line.

Also shown for context are values for surface and 

deep seawater at the Natural Energy Laboratory of Hawai‘i 

Authority (NELHA) facility at Keāhole, north of Honokōhau. 

These waters are used for ocean thermal energy conversion 

(OTEC) and aquaculture, and they are pumped from 55-in 

diameter pipelines offshore. NELHA surface seawater 

(SSW55) is from the solar-warmed, mixed surface layer 

of the ocean and is pumped from an intake depth of 79 ft. 

NELHA deep seawater (DSW55) is cold, subthermocline 

water pumped from an intake depth of 3,000 ft. Average 

temperatures for these NELHA seawaters are 26.2±0.20 °C 

for surface seawater and 5.64±0.35 °C for deep, subthermocline seawater. These temperatures are means and standard 

deviations of 57 measurements from August 2005 to June 

2010 (Olson, 2010). Oceanographic soundings offshore of 

NELHA have shown the warm, upper mixed layer to be about 

260 ft thick above the top of the thermocline (Campbell and 

Erlandson, 1979).

Figure 15. Graph showing temperature versus salinity for July 2009 water samples at KalokoHonokōhau National Historical Park, Island of Hawai‘i. Some samples lie well above the mixing line as 

a result of solar warming of open water bodies and water-distribution piping below hot pavement (in the 

case of the NPS tap water sample). NELHA, Natural Energy Laboratory of Hawai‘i Authority.

Honokōhau well 

NPS tap water 

KAHO 2 KAHO 1 

KAHO 3 

Kaloko fishpond G18 

‘Aimakapā fishpond A45 

Irrigation pond 

MW401

shallow 

MW400 

AP 144 

AP 53H 

AP 016 

AP 099 

MW401 deep (December) 

NELHA

deep

seawater

NELHA

surface

seawater

5 

10 

15 

20 

25 

30 

0 5 10 15 20 25 30 35 

Water temperature, in degrees Celsius 

Salinity 

July 2009 sample

Deep saline groundwater, December 2009

NELHA mean seawater, 2005-2010 

Hypothetical upland - deep saline groundwater mixing line 

EXPLANATION
26

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Many of the July values plot close to the mixing line 

shown in figure 15, including those for anchialine pool AP53H 

and all of the short-screened monitoring wells (KAHO 1, 

KAHO 2, KAHO 3, MW400, MW401 shallow). This is interpreted as supporting the basic mixing premise and the choice 

of end members. Samples whose values lie farther above the 

mixing line have a greater amount of the y-axis variable, in 

this case temperature, or heat. Samples with slight excess heat 

include anchialine pools AP 016 and AP 144, and Kaloko Fishpond G18. The anchialine pools are surrounded by black lava 

that warms in the sun and likely conducts heat to the shallow 

groundwater. Sample G18 at Kaloko Fishpond was collected 

at a known spring in the fishpond and presumably resembles 

other groundwater more than open pond water that has been 

subjected to solar warming or to mixing with warmer seawater 

that has entered through the fishpond rock wall.

Data points that lie well above the mixing line in figure 15

indicate large amounts of excess heat, and reasonable warming 

mechanisms can be postulated for each of these samples. 

NPS office tap water originates mostly from the Honokōhau 

well, with some fraction of its water contributed from another 

nearby well at times. The water at the well is cool, but by the 

time it reaches the NPS office it has been conveyed through 

miles of distribution piping beneath asphalt roadways heated 

by the subtropical sun. The Kohanaiki irrigation pond is an 

exposed pond with a black synthetic lining and is subject 

to direct solar warming; the warm temperature of the pond 

water sample suggests a long residence time and low flushing 

or turnover rate by new water, resulting in substantial solar 

warming (at least at the time of the sampling). At ʻAimakapā 

Fishpond A45, the warm sample may represent solar-warmed 

pond water rather than colder groundwater such as the Kaloko 

Fishpond G18 spring sample. Anchialine pool AP 099 is 

exposed to direct sun, having no overhead tree canopy such as 

at AP 144. It is also on a narrow peninsula, and it is conceivable that warm surface seawater is flushed in and out of the 

peninsula by the tides, mixing in with groundwater.

Extension of the mixing line in figure 15 to the right side 

of the graph (salinity=35) produces a y-intercept temperature 

of 16 °C, roughly midway between the NELHA surface- and 

deep-seawater reference values. Presuming that it is valid to 

extend the mixing line to estimate the temperature of fully 

saline groundwater, there are several plausible explanations 

for the intermediate temperature. One possibility is mixing of 

surface and deep seawater from offshore in the proper proportions that yield the intermediate temperature. Another possibility is a predominant influx of saltwater having that particular 

16 °C temperature, for example from a limited segment of the 

offshore submarine slope that intersects the oceanic thermocline at about that temperature. Finally, the saline groundwater may have originated mostly from colder subthermocline 

seawater and been warmed to 16 °C by geothermal heat within 

Figure 16. Graph showing temperature versus salinity for December 2009 water samples at KalokoHonokōhau National Historical Park, Island of Hawai‘i. Only three samples were measured the first day 

before the instrument malfunctioned. 

men14-5078_fig16

EXPLANATION

MW401

shallow 

MW401 deep 

MW400 

Honokōhau well (July) 

NELHA

deep

seawater

NELHA

surface

seawater

5 

10 

15 

20 

25 

30 

0 5 10 15 20 25 30 35 

Water temperature, in degrees Celsius 

Salinity 

December 2009 sample

Upland groundwater, July 2009

NELHA mean seawater, 2005–2010 

Hypothetical upland - deep saline groundwater mixing line 
Results and Interpretation 27

the flank of Hualālai Volcano. Remnant volcanic heat, particularly from the rift zone of the volcano, would tend to drive 

a thermal-convective flow of saltwater in and upward within 

the aquifer, much like the salt-entrainment-driven cyclic flow 

just beneath the brackish lens but potentially extending much 

deeper, perhaps to depths of thousands of feet within the 

mountain flank. Regardless of the exact origin, one important 

implication of the cold saline groundwater is that it is much 

higher in nutrients than surface seawater in the upper, mixed 

layer of the ocean where nutrients are stripped by phytoplankton uptake (Bienfang and Szyper, 1981).

Salinity did not change much from July to December at 

most sites (fig. 17). Exceptions were Kaloko Fishpond G18 

and Kohanaiki monitoring well MW400 (the closest to the 

ocean of the monitoring wells sampled), which showed opposite trends. Salinity at Kaloko Fishpond G18 was higher in 

December than in July, perhaps indicating a greater proportion 

of pond water over spring water in the sample, or a residual 

effect of the higher tide in December (fig. 14), even though 

the G18 sample was collected on the falling (hydrograph) 

limb near low tide. At MW400, the July sample had a higher 

salinity of 17 (about 50 percent seawater) and the December 

sample had a much lower salinity of 11.8. Average daily ocean 

level was about 0.5 ft lower during December sampling than 

in July (fig. 12), and the brackish coastal lens and water table 

will rise and fall with these ocean-level changes. MW400 is 

a short-screened monitoring well tapping salinity-stratified 

groundwater just below the water table. A 0.5-ft lowering of 

ocean and lens may have resulted in a greater proportion of the 

freshest, uppermost groundwater at the site in the December 

sample. Golf-course irrigation may also have contributed to 

the low salinity of the December sample, as discussed in the 

“Nutrients” section of this report.

Salinity and temperature profiles (fig. 18) from deep 

monitoring well MW401 at the north park boundary further 

reinforce Bowles (2007) finding that colder saltwater underlies 

a warmer brackish-water lens in the Kona area. Depth profiles 

of temperature and specific conductance (an electrical measure 

of salinity) were measured by NPS on December 7, 2009, a 

week after USGS sampling at the well on November 30 (profile data from Lindsey Kramer, National Park Service, written 

commun., 2011). The profile data—measured by NPS at many 

depths using a down-hole instrument—show that temperature decreases with depth in the well as specific conductance 

(salinity) increases. Values from two USGS water samples 

(especially the specific-conductance values) at -5 and -45 ft 

below the water table agree well with the profile data. Sample 

temperatures were 0.6–0.8 °C warmer than profile data at corresponding depths, perhaps reflecting an offset between NPS 

and USGS temperature sensors or warming of the sampled 

water during USGS sampling. 

The minimum temperature measured in the NPS profile 

was 17.0 °C, and the maximum specific conductance was 

45,970 μS/cm. This equates to a salinity of 29.8 (using the 

conversion formula of Wagner and others, 2006), or a saltwater fraction of 85 percent seawater. The maximum conductance recorded by NPS in monthly profiles from November 

2008 through February 2011was 47,800 μS/cm, corresponding 

to a salinity 31.1 or about 89 percent seawater (Rebecca Most, 

National Park Service, written commun., 2009). Apparently, 

the well is not deep enough to have reached 100 percent seawater within its depth of 116 ft below the water table (about 

115 ft below mean sea level). The deep USGS water sample in 

MW401 was about 67 percent seawater and had a temperature 

of 18 °C, colder than the 22 °C of fresh groundwater from the 

Honokōhau well far inland and much colder than the 26 °C of 

nearby NELHA surface seawater.

Similar temperature and salinity profiles have been measured in other monitoring wells near the Park. Bowles (2007) 

reported a minimum temperature of about 16 °C in a monitoring well southeast of Honokōhau Harbor and introduced 

a “cold saline groundwater” hypothesis in which saltwater 

below the top of the oceanic thermocline is able to flow readily into the aquifer through the steep submarine slope offshore. 

Cold saline water was worthy of note by Bowles because it ran 

counter to the general pattern at most other deep monitoring 

wells in Hawai ̒ i, where warmer saline groundwater underlies 

colder freshwater (for example Visher and Mink, 1964; Rotzoll, 2010). A more complex exception to the general pattern 

is the very deep KP-1 scientific borehole in Hilo, also on the 

island of Hawai ̒ i. Temperature profiles in this 3,465-ft deep 

borehole indicated cold, subthermocline saltwater of 5–7 °C 

temperature at depths greater than about 1,600 ft (Thomas and 

others, 1996). The well also penetrated two separate freshwater 

lenses, each grading into underlying saltwater: a shallow lens 

within the surficial Mauna Loa Volcano and a second lens in 

the underlying and older Mauna Kea Volcano. A second exception is a multi-aquifer configuration in Kona that is similar 

in some respects to that in Hilo. The Kamakana well, located 

roughly mid-slope between the coast and the Honokōhau well 

(fig. 1), was drilled from elevation 542 ft above sea level to 

1,220 ft below sea level. Salinity and temperature profiles in 

the well indicate a shallow brackish-water lens near sea level 

that is underlain by cold saline groundwater, much like the 

brackish lens at KAHO. However, the well encountered a 

second freshwater body at a depth of about 1,050 ft below sea 

level in what appears to be an underlying aquifer confined by 

poorly permeable rock and distinct from the surficial coastal 

aquifer (Tom Nance Water Resource Engineering, 2013).

One might question the choice of MW401 as the saline 

end member rather than, for example, surface seawater. However, the cold temperature of the MW401 sample and the NPS 

temperature profiles in figure 18 imply that saline groundwater 
28

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Figure 17. Graph showing change in salinity from July to December 2009 at Kaloko-Honokōhau National 

Historical Park, Island of Hawai‘i. Salinity was substantially higher in July at monitoring well MW400 and in 

December at Kaloko Fishpond G18. NELHA, Natural Energy Laboratory of Hawai‘i Authority.

men14-5078_fig17

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko fishpond G18 

‘Aimakapā fishpond A45 

Irrigation pond 

MW401 shallow 

MW400 

AP 144 

AP 53H AP 016 

AP 099 

0 

5 

10 

15 

20 

0 5 10 15 20 

Salinity in December 2009 

Salinity in July 2009 

Higher in December 

Higher in July 

Line of 1:1 slope (no change) 

Figure 18. Graph showing depth profiles of temperature and specific conductance in Kohanaiki 

monitoring well MW401, Island of Hawai‘i, December 7, 2009, and USGS water samples one week 

earlier on November 30. Sample values coincided reasonably well with the profiles, although the water 

samples were 0.4–0.7 °C warmer than the temperature profile. Profile data are from Lindsey Kramer, 

National Park Service, written commun., 2011).

16 17 18 19 20 21 22 23

0

20

40

60

80

100

120

0

20

40

60

80

100

120

Water temperature, in degrees Celsius

Water sample at -5 feet Water sample 0.8 degree 

Celsius warmer than profile 

Water sample at -45 feet

15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000

Depth, in feet below the water table

Specific conductance, in microSiemens per centimeter at 25 degrees Celsius

Water sample 0.6 degrees 

Celsius warmer than profile 

EXPLANATION

USGS sample specific conductance, Nov. 30, 2009

USGS sample temperature, Nov. 30, 2009

NPS specific conductance profile, Dec. 7, 2009

NPS temperature profile, Dec. 7, 2009
Results and Interpretation 29

at KAHO cannot originate solely from warm surface seawater, 

a large fraction of cold, subthermocline seawater must be present to explain the temperatures. The precise relevance of the 

NELHA surface and deep seawaters to environmental waters 

at KAHO can only be inferred, whereas the deep MW401 

sample from immediately beneath the brackish-water lens in 

the vicinity of the other samples is unquestionably of more 

local relevance and so was chosen as the saline end member 

for the dataset.

To summarize, plotting of salinity and temperature 

data for the July and December 2009 water samples allows 

the samples to be interpreted with respect to a hypothetical 

conservative mixing line between fresh upland groundwater 

from Honokōhau well and cold saline groundwater beneath 

the brackish-water lens (best sampled at monitoring well 

MW401). Data from the monitoring wells and from most 

anchialine pools plot close to the hypothetical mixing line, 

whereas data from tap water and the larger ponds plot well 

above the mixing line and can be explained reasonably by 

direct solar warming or by mixing with nearby warm surface 

seawater (AP 099). A similar approach to graphical interpretation is taken (later in this report) with other constituents such 

as nutrients and isotopic compositions.

Stable Isotopes of Water

Stable isotopes of water further support the hypothesis 

that most samples are plausible mixtures of upland groundwater and saline water. A slight shift of most samples off of a 

hypothetical mixing line may indicate that mid-slope recharge 

contributing to the low-elevation samples may differ isotopically from upland recharge that determines the composition of 

the freshwater end member at the Honokōhau well.

Plots of δ2H and δ18O isotopic compositions are shown 

in figures 19 and 20 for July and December samples, respectively. Most of the data fall close to the hypothetical mixing 

line, having intermediate compositions between those of the 

Honokōhau well and MW401 deep; therefore most samples 

are plausible mixtures of the fresh and saline end members to a 

first approximation. NPS office tap water is distinctly isotopically heavier (more positive) than Honokōhau well water, suggesting that it has some fraction of water from another source 

blended in, perhaps from Keahuola QLT 1 well (fig. 1) as discussed earlier. The NELHA seawater values plot close to the 

mixing line where the line is extended to the upper right (note 

that the NELHA values for isotopic composition span a much 

shorter time than for temperature, roughly 1.5 months in late 

2009). The July and December plots do not differ dramatically, 

with the greatest shifts in composition being the two fishpond 

samples, Kaloko and ʻAimakapā Fishponds. Plots of most of 

the samples fall slightly above the mixing line, indicating that 

they are slightly heavier in δ2H composition than would be 

predicted by simple mixing between Honokōhau well water 

and deep saline groundwater. An alternate approach would be 

to draw the mixing line through the NELHA seawater symbols 

for a true seawater end member, and in that case MW401 deep 

would plot slightly above that line like the other samples.

Nutrients

Nitrogen and phosphorus in most water samples in and 

near the Park were enriched in comparison to expected background concentrations along a freshwater-saltwater mixing 

line. Most nutrient enrichments were less than 60 percent, but 

three sites along the north boundary of the Park (anchialine 

pool AP 144 and monitoring wells MW400 and MW401) had 

nitrogen enrichments of 75, 110, and 280 percent above background that can be attributed to fertilizer application during an 

initial turf grow-in period when vegetation was being established at the adjacent resort golf course. Combined nitrogen 

and phosphorus enrichments at monitoring wells closest to 

Kaloko Light Industrial Park may indicate septic contamination in that vicinity.

Nitrogen

Dissolved inorganic nitrogen (DIN=NH3+NO2+NO3) 

is plotted against salinity in figures 21 and 22 for July and 

December water samples, respectively, in order to interpret the 

various brackish waters across their range in salinity. As was 

done for water temperature, most water samples are assumed 

to have originated as mixtures of fresh and saline groundwater 

end members, and a mixing line is drawn between the upland 

freshwater sample from the Honokōhau well and the deep 

saline water sample from 45 ft below the water table in monitoring well MW401. With regard to nutrients, both of these 

waters can be thought of as representing “natural background” 

conditions subject to minimal anthropogenic addition of 

nutrients. The Honokōhau well is located high on the mountain flank above most developed lands, and fresh groundwater 

from the well was recharged mostly through forested and 

grassy uplands. DIN concentration at the Honokōhau well was 

1,160 μg/L (table 3), closely comparable to the average nitrate 

concentration of 1,148 μg/L for 22 samples from the same 

well (Bienfang, 2008) and the 1,170 μg/L background nitrate 

concentration for the similarly arid Kīhei uplands on Maui 

(Hunt, 2007). The deep saline-water sample from monitoring 

well MW401 had a DIN concentration of 647 μg/L (table 4).

Samples plotting above the mixing line in figures 21 

and 22 are interpreted as being enriched in nitrogen above 

background concentrations; that is, nitrogen has been added 

from some source in comparison to simple mixing of the 

end-member upland and saline background waters. Similarly, 

samples plotting below the mixing line are interpreted as being 

depleted in nitrogen (nitrogen has been removed by some 

mechanism). The amount of enrichment or depletion can be 

expressed in concentration units above or below the mixing 

line, or as a percentage of the mixing line DIN concentration 

at that point along the salinity scale.
30

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

The highest DIN concentration measured was 3,660 μg/L 

at monitoring well MW401 in July (fig. 21), in a water sample 

pumped from 5 ft below the water table. This corresponds to 

an apparent enrichment of 2,700 μg/L or 280 percent above 

the expected background concentration of 960 μg/L on the 

mixing line (mixing-line concentrations were estimated 

graphically, by scaling vertical heights above the hypothetical 

mixing line against the y-axis). 

Brock (2010) monitored water quality for The Shores 

at Kohanaiki during this time period and measured increasing nitrogen concentrations from 2007 through early 2009 in 

anchialine pools and marine waters that he sampled. Brock 

attributed the elevated nitrogen to fertilization and watering of 

golf course landscaping during the “turf grow-in” period necessary to establish the vegetation. Brock also described later 

declines in nitrogen as the grow-in period waned (it concluded 

in October 2009) and fertilizer application and watering were 

reduced. Monitoring well MW401 is on the Kohanaiki property, immediately adjacent to such landscaping, and the depth 

to the water table is only 18 ft. It is apparent that excess nitrogen from fertilizers leached into groundwater at Kohanaiki 

and was reflected in the July water sample from MW401. The 

acute nitrogen enrichment at MW401 appears to have been 

temporary, however, and by December (fig. 22) DIN concentration at MW401 had fallen to 2,010 μg/L. This represents a 

45 percent decline from July, though the December concentration was still enriched by 1,050 μg/L or 109 percent above the 

mixing-line background concentration.

The second highest DIN concentration in July was 

1,480 μg/L at AP 144, an apparent enrichment of 630 μg/L or 

75 percent above the background concentration of 845 μg/L at 

the mixing line. Anchialine pool AP 144 is very near the north 

park boundary and may have experienced the same nitrogen 

enrichment from fertilizers as MW401. Alternately, the apparent nitrogen enrichment at AP 144 could be a result of biotic 

cycling, as this pool hosts a large population of endemic 

shrimp that were seen on all site visits.

Monitoring well MW400 is just a short distance away 

from AP 144, but it did not show a similar DIN enrichment in 

July (fig. 21). However, by December DIN concentration at 

MW400 had risen to 1,900 μg/L, an enrichment of 1,000 μg/L 

or 111 percent above the estimated background concentration of 900 μg/L at the mixing line (fig. 22). A small part of 

the DIN increase at MW400 can be attributed to the sharp 

decline in salinity from July to December, from 17 to 11.8 

(tables 3, 4). The greater fraction of freshwater in the December sample would have been accompanied by a slight increase 

in DIN, but only along a trend paralleling the mixing line if 

the only change was the degree of freshwater-saltwater mixing. Instead, the considerable vertical displacement of MW400 

off of the mixing line in the December plot requires a large 

addition of DIN, over and above what can be attributed to 

freshwater-saltwater mixing. One possible source is the same 

fertilizer-derived nitrogen as at MW401 but delayed, perhaps, 

as a plume of fertilizer-enriched groundwater flowed shoreward from MW401 to MW400 over the intervening months. 

The lower salinity of the December sample at MW400 could 

also be a marker of landscape irrigation water: infiltration 

of freshwater from excess irrigation would tend to dilute the 

ambient brackish groundwater in the vicinity, as well as carry 

fertilizer-derived nutrients downward and shoreward.

Remaining sites had DIN concentrations less than 

1,500 μg/L and DIN enrichments within about 300 μg/L 

of the mixing line, or no more than 30 to 40 percent above 

background concentrations. DIN concentration at monitoring 

well KAHO 1 plotted right on the mixing line in July (fig. 21), 

but by December DIN had risen to 1,330 μg/L (fig. 22), an 

enrichment of 380 μg/L or 40 percent above the estimated 

background concentration of 950 μg/L at the mixing line. As 

was true at MW400, a drop in salinity at KAHO 1 from July 

to December may account for a small part of the increase in 

DIN, but simple dilution by freshwater would have shifted its 

plotting position along the mixing line. Instead, movement of 

the data point well off the mixing line in figure 22 implies that 

there was a substantial addition of nitrogen.

A potentially key observation at KAHO 1 was that 

hydrogen sulfide gas was detected by smell in July, indicating sulfate-reducing and denitrifying conditions in the aquifer. 

Sulfate reduction is an intermediate step in a sequence of 

bacterially catalyzed redox reactions and is preceded by 

nitrate reduction, which itself is preceded by oxic respiration 

(Schwarzenbach, Gschwend, and Imboden, 2002). Active 

denitrification could mean that the July DIN concentration 

at KAHO 1 was diminished somewhat in at least part of the 

aquifer contributing to the well. If this is true, the higher DIN 

concentration in December may be more generally indicative 

of the site’s usual nitrogen state – that is, about 40 percent 

enriched above the expected DIN background concentration at 

the mixing line.

Furthermore, these redox reactions typically proceed by 

bacterial consumption of organic carbon, sequentially utilizing 

and depleting oxygen, nitrogen, and sulfate in the process. The 

presence of hydrogen sulfide at KAHO 1 suggests a source 

of organic carbon in the aquifer that would promote the chain 

of redox reactions. One possible source of organic carbon is 

septic waste. The nearby KAHO visitor center (about 150 ft 

uphill from KAHO 1) has restrooms but has never had an 

onsite septic system; instead, it has been connected to a stem 

line of the regional sewer system since the center opened in 

2003 (Sallie Beavers, National Park Service, oral commun., 

2014). Somewhat farther away are various septic systems 

at Kaloko Light Industrial Park, across the highway to the 

northeast (fig. 3). The Industrial Park is not directly uphill 

from KAHO 1, but Bowles and others (2006) show a conceptual model of regional groundwater convergence toward 

Honokōhau Harbor, raising the possibility that groundwater 

from beneath the Industrial Park may plausibly be drawn 

southwest toward KAHO 1 by that flow convergence. The harbor was excavated into the aquifer a lateral distance of 0.4 mi 

from the pre-existing shore and is thought to act as a regional 

drain, preferentially focusing groundwater discharge there.
Results and Interpretation 31

Figure 19. Graph showing δ2H versus δ18O for July 2009 water samples at KalokoHonokōhau National Historical Park, Island of Hawai‘i. Most samples fall close to a 

hypothetical mixing line between freshwater (Honokōhau well) and seawater (NELHA). 

NELHA, Natural Energy Laboratory of Hawai‘i Authority.

men14-5078_fig19

Honokōhau well 

NPS tap

water 

KAHO 1, AP 53H 

KAHO 2 

KAHO 3 

‘Aimakapā

fishpond

A45 

Irrigation pond 

MW401 shallow 

MW400 

AP 144,

Kaloko

fishpond

G18 

AP 016 

AP 099 MW401 deep (December) 

NELHA

deep

seawater 

NELHA

surface

seawater 

-45 

-40 

-35 

-30 

-25 

-20 

-15 

-10 

-5 

0 

5 

-7 -6 -5 -4 -3 -2 -1 0 1 

δ2H of water, in per mil 

δ18O of water, in per mil 

July 2009 sample

Deep saline groundwater, December 2009

NELHA mean seawater, Oct 11 to Dec 1, 2009 Hypothetical upland - deep saline groundwater mixing line 

EXPLANATION

Figure 20. Graph showing δ2H versus δ18O for December 2009 water samples at 

Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Most samples fall close to 

a hypothetical mixing line between freshwater (Honokōhau well) and seawater (NELHA). 

NELHA, Natural Energy Laboratory of Hawai‘i Authority.

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko fishpond G18 

‘Aimakapā

fishpond

A45

Irrigation pond 

MW401 shallow 

MW401 deep 

MW400 

AP 144 

AP 53H AP 016 

AP 099 

Honokōhau well (July) 

NELHA

deep

seawater

NELHA

surface

seawater

-45 

-40 

-35 

-30 

-25 

-20 

-15 

-10 

-5 

0 

5 

-7 -6 -5 -4 -3 -2 -1 0 1 

δ2H of water, in per mil 

δ18O of water, in per mil 

December 2009 sample

Upland groundwater, July 2009 Hypothetical upland - deep saline groundwater mixing line 

NELHA mean seawater, Oct 11 to Dec 1, 2009 

EXPLANATION
32

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Figure 21. Graph showing dissolved inorganic nitrogen (DIN) versus salinity for July 2009 

water samples at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Acute DIN 

enrichment at MW401 was likely caused by fertilizer applied nearby. NELHA, Natural Energy 

Laboratory of Hawai‘i Authority.

men14-5078_fig21

Honokōhau well 

NPS tap water 

KAHO 1 

KAHO 2 KAHO 3 

Kaloko

fishpond

G18 

‘Aimakapā fishpond A45 

Irrigation pond 

MW401 shallow 

MW400 

AP 144 

AP 53H 

AP 016 

AP099 MW401 deep (December) 

NELHA

deep

seawater 

NELHA surface seawater 

0 

50 

100 

150 

200 

250 

0 

1,000 

2,000 

3,000 

4,000 

0 5 10 15 20 25 30 35 

Dissolved inorganic nitrogen (DIN), in micromoles per liter as N

Dissolved inorganic nitrogen (DIN), in micrograms per liter as N

Salinity, in July 2009 

July 2009 sample

Deep saline groundwater, December 2009

NELHA mean seawater, 2005-2010 

Greatest apparent enrichment 

approximately 2,700 μg/L (193 μ M/L) 

above hypothetical mixing line 

Hypothetical upland - deep saline groundwater mixing line 

EXPLANATION

Figure 22. Graph showing dissolved inorganic nitrogen (DIN) versus salinity for December 

2009 water samples at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. DIN 

concentration at MW401 shallow dropped by nearly half (45 percent) from July. NELHA, 

Natural Energy Laboratory of Hawai‘i Authority.

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko fishpond G18 

Irrigation pond ‘Aimakapā fishpond A45 

MW401 shallow 

MW401 deep 

MW400 

AP 144 

AP 53H 

AP 016 

AP 099 

Honokōhau

well (July) 

NELHA deep seawater 

NELHA surface seawater 

0 

50 

100 

150 

200 

250 

0 

1,000 

2,000 

3,000 

4,000 

0 5 10 15 20 25 30 35 

Dissolved inorganic nitrogen (DIN), in micromoles per liter as N

Dissolved inorganic nitrogen (DIN), in micrograms per liter as N

Salinity, in December 2009 

December 2009 samples

Upland groundwater, July 2009

NELHA mean seawater, 2005-2010 

Greatest apparent enrichment approximately 1,050 μg/L (75 μ M/L) 

above hypothetical mixing line 

Hypothetical upland - deep saline groundwater mixing line 

EXPLANATION
Results and Interpretation 33

Some water samples showed DIN depletion from the 

mixing line; these include ʻAimakapā Fishpond in July 

(fig. 21) and both ʻAimakapā and Kaloko Fishponds in 

December (fig. 22). Possible mechanisms for depletion of 

DIN in the fishponds include biotic uptake (assimilation) 

by phytoplankton and aquatic plants, and sequestration and 

denitrification in muddy bottom sediments. Simple dilution of 

DIN could also result from incursion of low-nutrient surface 

seawater, but only in Kaloko Fishpond through the opening 

in its seaward rock wall. Kohanaiki irrigation pond had very 

low DIN concentrations in both July and December. This is 

an expected result because this water has been produced by 

reverse-osmosis (RO) desalination, which removes most dissolved constituents including nitrogen and phosphorus.

Changes in DIN concentration from July to December for 

sites sampled both times are shown in figure 23. The greatest 

changes in groundwater samples were at MW401, where DIN 

was much higher in July and declined sharply by December; 

and at MW400, where DIN was much lower in July and 

increased sharply by December. Lesser changes were observed 

at anchialine pool AP 144 (DIN higher in July) and monitoring 

well KAHO 1 (DIN higher in December). In the ʻAimakapā 

and Kaloko Fishponds, respectively, DIN concentrations 

declined from 617 and 809 μg/L in July to 44 and 215 μg/L 

in December.

For comparison purposes, nitrogen concentration in the 

water sample from the upland Honokōhau well (1,160 μg/L) 

was essentially identical to that in a sample from an upland 

well (1,170 μg/L) in the similarly dry Kīhei area of Maui 

(Hunt, 2007). Nitrogen concentrations were much less in the 

Park than in intensively agricultural areas such as Lahaina, 

Maui (Soicher and Peterson, 1997) or central Oahu (Hunt, 

2004), where nitrate concentrations (ranging from 2,000–

5,000 μg/L) have historically been 2 to 4 times greater than at 

KAHO as a result of agricultural fertilizer use.

Phosphorus

Phosphorus concentrations (orthophosphate PO4, as P) 

are plotted against salinity in figures 24 and 25 for July and 

December samples, respectively. Phosphorus concentrations 

were less than 180 μg/L and were about an order of magnitude lower than nitrogen concentrations. This is typical, and 

is largely because phosphorus has a strong tendency to sorb 

to soil and mineral surfaces and is therefore less likely to 

leach into groundwater than nitrogen. As was done for DIN, 

samples are interpreted by their distance above or below 

the mixing line (enriched or depleted in comparison to the 

upland-deep saline groundwater mixing line), and enrichments are expressed in concentration units or as a percentage 

of the mixing-line concentration, which is considered the 

background concentration in mixtures of the fresh and saline 

end-member waters.

The greatest apparent phosphorus enrichments were at 

monitoring wells KAHO 2 in July and KAHO 1 in December. 

The July PO4 concentration at KAHO 2 was 177 μg/L, an 

enrichment of 55 μg/L or 45 percent above the mixing-line 

concentration of 122 μg/L. The December PO4 concentration at KAHO 1 was 171 μg/L, an enrichment of 62 μg/L or 

57 percent above the mixing-line concentration of 109 μg/L. 

Other notable but slightly lesser enrichments were at monitoring well KAHO 3 and anchialine pools AP 53H and AP 016. 

All of these sites are downslope from or near Kaloko Light 

Industrial Park (fig. 3), particularly KAHO 2, and their 

elevated phosphorus concentrations may reflect some fraction 

of septic leachate in the water samples. 

Also notable in figures 24 and 25 is that plots of PO4

concentrations for MW400, MW401, and AP 144 lie near 

the mixing line and show no more than slight enrichment in 

contrast to the high DIN enrichments from fertilizer at those 

sites (figs. 21, 22). Nitrogen in fertilizer is readily leached to 

groundwater, but phosphorus is not because it tends to sorb 

to soil where the fertilizer is applied. Although true, this may 

not be the entire reason that phosphorus was not elevated to 

nearly the same degree as nitrogen at these sites. Another factor is that many fertilizers are richer in nitrogen than phosphorus, and landscaping specialists may have tailored fertilizer proportions to be much more heavily weighted toward 

nitrogen over phosphorus for the purpose of establishing the 

golf-course vegetation.

Changes in PO4 from July to December at sites sampled 

both times are shown in figure 26. Sites with substantially 

higher PO4 concentrations in December were KAHO 1 and 

MW400. December salinity was lower in these samples than 

in July, and by accounting for translation along the mixing 

trend in figures 24 and 25, it is estimated that the lower 

salinity can account for the entire 20 μg/L increase in PO4 at 

MW400 from July to December, but only about 10 μg/L of the 

34 μg/L increase in PO4 at KAHO 1, with the remainder presumably representing a real addition of phosphorus over July.

Kaloko and ʻAimakapā Fishponds had substantially 

higher PO4 concentrations in July than in December (fig. 26), 

but this is more a function of their December concentrations 

apparently being depleted: their PO4 concentrations plot 

on or near the mixing line in figure 24 but well below the 

mixing line in figure 25. The low December PO4 concentrations corresponded with similarly low DIN concentrations 

in December (fig. 23), suggesting depletion mechanisms at 

work for both nutrients, the most likely being biotic uptake 

of N and P by phytoplankton and denitrification of nitrate in 

pond-bottom muds.

Nutrient Implications of the Cold Saline 

Groundwater

Saline groundwater beneath the brackish groundwater 

lens at KAHO is both colder and much higher in nutrients than 

surface seawater in the upper mixed layer of the ocean around 

Hawai ̒ i. The single deep groundwater sample from monitoring 

well MW401 had a temperature of 18 °C, and projection of the 

mixing line plotted on figure 15 to the right axis (salinity = 35) 
34

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Figure 23. Graph showing change in dissolved inorganic nitrogen (DIN) from July to December 

2009 at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Changes at MW401 and 

MW400 were associated with fertilizer; changes at Kaloko and ʻAimakapā Fishponds likely reflect 

greater nitrogen uptake by phytoplankton in December.

men14-5078_fig23

KAHO 1 KAHO 2 

KAHO 3 

Kaloko fishpond G18 ‘Aimakapā

fishpond A45 

Irrigation

pond 

MW401 shallow 

MW400 

AP 144 

AP 53H 

AP 016 

AP 099

0 

1,000 

2,000 

3,000 

4,000 

0 1,000 2,000 3,000 4,000 

Dissolved inorganic nitrogen (DIN) in December 2009, in micrograms per liter as N

Dissolved inorganic nitrogen (DIN) in July 2009, in micrograms per liter as N

Higher in December 

Higher in July 

Line of 1:1 slope (no change) 

Figure 24. Graph showing orthophosphate versus salinity for July 2009 water samples 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Sites showing greatest 

enrichment (KAHO 1, KAHO 2, KAHO 3, AP 016, AP 53H) lie near and downslope from 

Kaloko Light Industrial Park and the KAHO visitor center. NELHA, Natural Energy Laboratory 

of Hawai‘i Authority.

Honokōhau well 

NPS

tap water 

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko fishpond G18 

‘Aimakapā fishpond A45 

Irrigation pond 

MW401 shallow 

MW400 

AP 144 

AP 53H 

AP 016 

AP 099 

MW401 deep (December) 

NELHA

deep

seawater 

NELHA surface seawater 

0 

1 

2 

3 

4 

5 

6 

7 

8 

0 

50 

100 

150 

200 

250 

0 5 10 15 20 25 30 35 

Orthophosphate (PO4), in micromoles per liter as P 

Orthophosphate (PO4), in micrograms per liter as P 

Salinity, in July 2009 

July 2009 sample

Deep saline groundwater, December 2009

NELHA mean seawater, 2005-2010 

Greatest apparent enrichment approximately 55 μg/L (1.8 μ M/L) above hypothetical mixing line 

Hypothetical upland - deep saline groundwater mixing line 

EXPLANATION
Results and Interpretation 35

Figure 25. Graph showing orthophosphate versus salinity for December 2009 water 

samples at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Sites showing 

greatest enrichment (KAHO 1, KAHO 2, KAHO 3, AP 016, AP 53H) lie near and downslope 

from Kaloko Light Industrial Park and the KAHO visitor center. NELHA, Natural Energy 

Laboratory of Hawai‘i Authority.

men14-5078_fig25

KAHO 1 KAHO 2 

KAHO 3 

Kaloko fishpond G18 

‘Aimakapā fishpond A45 

Irrigation pond 

MW401

shallow

MW401 deep 

MW400 

AP 144 

AP 53H 

AP 016 

AP 099 

Honokōhau well (July) 

NELHA

deep

seawater

NELHA surface seawater 

0 

50 

100 

150 

200 

250 

0 5 10 15 20 25 30 35 

Orthophosphate (PO4), in micromoles per liter as P

Orthophosphate (PO4), in micrograms per liter as P

Salinity, in December 2009 

December 2009 sample

Upland groundwater, July 2009

NELHA mean seawater, 2005-2010 

Greatest apparent enrichment approximately 62 μg/L (1.9 μ M/L) above hypothetical mixing line 

Hypothetical upland - deep saline groundwater mixing line 

EXPLANATION

8

7

6

5

4

3

2

1

0

Figure 26. Graph showing change in orthophosphate from July to December 2009 at KalokoHonokōhau National Historical Park, Island of Hawai‘i. Concentrations in Kaloko and ʻAimakapā 

Fishponds were higher in July; lower December concentrations may reflect greater phosphorus 

uptake by phytoplankton.

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko fishpond G18 

‘Aimakapā fishpond A45 

Irrigation pond 

MW401 shallow MW400 

AP 144 

AP 53H 

AP 016 

AP 099 

0 

50 

100 

150 

200 

0 50 100 150 200 

Orthophosphate (PO4

) in December 2009, in micrograms per liter as P

Orthophosphate (PO4) in July 2009, in micrograms per liter as P 

Higher in December 

Higher in July Line of 1:1 slope (no change) 
36

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

yields an estimate of 16 °C for fully saline groundwater. Temperatures this cold require that the saline groundwater contain 

a large fraction of cold subthermocline seawater, which is 

known to be much higher in nutrients than surface seawater. 

Average nutrient concentrations for NELHA surface seawater 

are 12 μg/L DIN and 4.2 μg/L PO4 whereas corresponding 

averages for NELHA deep seawater are 590 μg/L DIN and 

91 μg/L PO4 (means of 56 measurements from 2005–10; 

Olson, 2010). The lower values illustrate the “nutrient-poor” 

character of surface seawater in the upper mixed layer of 

the ocean around Hawai ̒ i, where nutrients are assimilated 

by phytoplankton (Bienfang and Szyper, 1981). In contrast, 

the higher values for NELHA deep seawater illustrate that 

subthermocline seawater is much more enriched in nutrients 

than surface seawater.

For nitrogen, extension of the mixing line in figure 21 to 

the right axis (salinity = 35) results in a y-intercept of about 

400 μg/L DIN, less than the DIN in NELHA deep seawater 

(590 μg/L) but 33 times greater than the DIN in NELHA surface seawater (12 μg/L). Similarly for phosphorus, extension 

of the mixing line in figure 24 results in a y-intercept of about 

25 μg/L PO4, roughly one-quarter of the PO4 in NELHA deep 

seawater (91 μg/L) but still 6 times the PO4 in NELHA surface 

seawater (4.2 μg/L).

These comparisons illustrate that ecologic interpretations 

in the brackish-water environment at KAHO (and similar areas 

are where cold saline groundwater exists) require awareness 

of the higher nutrient content of the colder seawater. This 

runs counter to general experience with shallow freshwatersaltwater mixing environments in Hawai ̒ i, where one can 

usually assume nutrient-poor surface seawater as a saltwater 

end-member having nutrient concentrations that are nearly 

negligible in comparison to much higher concentrations in terrestrial fresh groundwater. Additional sampling to better characterize the cold saline groundwater is warranted, for example, 

by testing groundwater samples from other deep wells on the 

Kona coast and from deeper in monitoring well MW401 than 

was able to be sampled.

Stable Isotopes of Nitrate for Nitrate 

Source Identification

Nitrate stable isotopes (tables 3, 4) did not compellingly implicate septic nitrogen in KAHO groundwater in the 

expected way: by water samples having nitrate δ15N values on 

the order of +10 per mil or more that would exceed the range 

for natural soil nitrogen (fig. 9) and be more strongly diagnostic of waste nitrogen. In fact, the heaviest δ15N values of about 

6.6, 7.7, and 6.4 per mil were in Kaloko Fishpond, ʻAimakapā 

Fishpond, and Kohanaiki irrigation pond, respectively (table 4),

where they corresponded with low nitrate concentrations. This 

pairing of low nitrate concentration and heavy nitrate isotopic 

composition is likely to have resulted from nitrate removal by 

biochemical cycling such as biotic uptake and denitrification. 

Most remaining water samples had nitrate δ15N values from 

+3 to +5 per mil, heavier than the value of +2 per mil in the 

upland Honokōhau well, but still plotting in an area on figure 

9 where natural soil nitrogen and waste nitrogen fields overlap 

and the two nitrogen sources cannot be distinguished.

Prior studies of septic-system and municipal wastewaters 

provide points of comparison for judging possible wastewater 

presence in KAHO water samples (table 6). Aravena and others (1993) sampled leachate from a single household septic 

system and found δ15N = +10 per mil and a nitrogen concentration of 30,000 μg/L as N. Municipal wastewater treatment 

plants tend to drive the already heavy isotopic composition of 

raw sewage even heavier by microbial action during treatment, 

especially if the plant incorporates advanced nitrogen removal 

using anoxic, denitrifying lagoons. If these treated effluents 

are disposed by injection wells, further denitrification tends to 

take place in the aquifer, driving isotopic compositions heavier 

still and making nitrogen isotopes very good tracers of municipal wastewater in the environment. Three examples from 

Hawai‘i wastewater treatment plants bear this out (table 6): 

Kealakehe, Kona (δ15N = +12 per mil in treated wastewater, 

+20 per mil in the aquifer); Kīhei, Maui (δ15N = +15 per mil in 

treated wastewater, +23 per mil in the aquifer); and Lahaina, 

Maui (δ15N = +23 per mil in treated wastewater, +40 per mil in 

the aquifer). In contrast, groundwater from wells uphill of the 

wastewater injection plumes had lighter δ15N values, ranging 

from +1 to +5 per mil that lie within the range for natural soil 

nitrogen (fig. 9).

Nitrate stable isotope compositions are shown graphically 

in figure 27 for July 2009 water samples at KAHO. Samples 

plotting up or to the right of other samples may reflect addition of isotopically heavier nitrate or may reflect evolution to 

heavier isotopic values through processes that deplete nitrate, 

like denitrification and biotic uptake. The isotopically lightest samples were NPS office tap water and the Honokōhau 

well, the upland background end member with δ15N = +2 per 

mil and δ18O = +0.4 per mil. Most other samples cluster in 

the bottom half of the graph with δ15N ranging between +3 

and +5 per mil and δ18O ranging between 0 and +4 per mil. 

The slightly heavier isotopic compositions of these samples in 

comparison to the Honokōhau well sample may reflect addition of isotopically heavier nitrate as groundwater flowed from 

the uplands to these locations. This is plausible because many 

of these samples plot above the upland-deep saline groundwater mixing line in figure 21, indicating some addition of 

nitrogen over and above the DIN concentration in freshwater 

from the Honokōhau well. The sample with the heaviest δ15N 

in July was ʻAimakapā Fishpond with δ15N = +6.16 per mil. 

Also shown in figure 27 are two sets of parallel lines, 

with slope 1:2 (gray) representing possible denitrification 

trends and slope 1:1 (blue) representing possible uptake or 

assimilation of nitrate by phytoplankton. Samples plotting 

along trend up and to the right of another sample could conceivably have evolved from the other sample’s composition by 

denitrification or biotic uptake, but only if (1) the map location 

of the samples makes one water a plausible parent for the 

other; (2) nitrate concentration is lower in the evolved sample 
Results and Interpretation 37

than in the parent water; and (3) nitrate concentration in the 

evolved sample is commensurately lower. “Commensurately” 

means that the observed reduction in nitrate concentration is 

proportionate with the observed amount of isotopic enrichment toward the heavier isotopes, as governed by Rayleigh 

equations with accepted enrichment factors from the scientific literature (for example, Kendall and McDonnell, 1998). 

An in-depth analysis using Rayleigh calculations is beyond 

the scope of this project and would be best carried out by an 

isotope specialist. A few trial calculations for presumed pairs 

of parent-daughter waters yielded enrichment factors outside 

the range of published values. Furthermore, several processes 

may have been active and cannot readily be distinguished by 

simple calculations that assume a single process. Therefore, 

only conditions (1) and (2) will be noted from here on.

An example of a possible denitrified sample is ʻAimakapā 

Fishpond in July, which plots roughly along a denitrification 

trend from KAHO 1 in figure 27. Groundwater at KAHO 1 

is a plausible parent water because KAHO 1 lies just uphill 

from ʻAimakapā Fishpond (fig. 3) and groundwater in that 

vicinity is expected to discharge to the pond. DIN is lower 

in ʻAimakapā Fishpond than in KAHO 1 and by some cause 

other than dilution, because the ʻAimakapā Fishpond sample 

does not lie along the upland-deep saline groundwater mixing 

line in figure 21 for the July samples. Instead, the ʻAimakapā 

sample has nearly the same salinity as KAHO 1, but has less 

nitrate and plots below the mixing line.

The sample with heaviest δ18O in nitrate was monitoring well MW401, plotted near the top of figure 27 with δ18O 

= +5.50 per mil. Recall from the nitrate source classification 

in figure 9 that nitrate fertilizer has heavier δ18O than most 

other nitrate sources, and that MW401 had a high concentration of likely fertilizer-derived nitrogen in July (fig. 21). Also 

lying in the direction of MW401 on figure 27 are the AP 144 

and Kaloko Fishpond G18 samples, suggesting that they also 

contain some fraction of fertilizer nitrate. This is plausible 

because they are close to and downgradient from MW401. It 

is unknown why the δ18O value of +5.50 per mil at MW401 

is not closer to the value of +20 per mil in figure 9, although 

several possible reasons can be proposed. Foremost is that 

roughly one third of the nitrate in the MW401 sample is likely 

to be upland background nitrate, expected in all groundwater 

samples and having a δ18O composition close to zero, judging 

by the near-zero δ18O value at the Honokōhau well. Secondly, 

it’s possible that not all the fertilizer applied was nitrate mineral fertilizer. Manure or urea fertilizers may also have been 

applied and contributed to a δ18O composition lighter than 

+20 per mil.

Interpretation is aided further by plotting nitrate concentration against δ15N of nitrate for July samples in figure 28. 

Table 6. Nitrate stable-isotope compositions of wastewater sources for comparison to results of this study.

[TDN, total dissolved nitrogen, including both organic and inorganic forms; DIN, dissolved inorganic nitrogen; TDP, total dissolved phosphorus, including both 

organic and inorganic forms; PO4, orthophosphate, the predominant form of dissolved inorganic phosphorus; per mil, parts per thousand; μg/L, micrograms per 

liter; –, not applicable]

Location and type of water 

sample

δ15N of 

nitrate 

(per mil)

δ18O of 

nitrate 

(per mil)

TDNa or 

DINb

(μg/L)

TDPa or 

PO4

b

(μg/L)

Remarks

Household septic system effluent1 10 3.4 30,000b – –

Honokōhau upland background well2 2 0 1,160b 140b Uplands are mostly forest and grassland

Kealakehe, treated wastewater3 12 0 3,750a 5,080a Secondary-treated wastewater

Kealakehe, well in wastewater plume3 20 4 1,490a 3,100a Monitoring well

Kīhei, upland background well4 5 1 1,170a 67a Uplands are mostly scrub forest with some 

ranch pasture

Kīhei, treated wastewater4 15 8 7,330a 1,720a Tertiary-treated wastewater

Kīhei, well in wastewater plume4 23 11 3,490a 191a Household irrigation well

Lahaina, upland background well5 1 3 3,560b 240b High DIN from former sugarcane cultivation

Lahaina, treated wastewater5 23 8 6,120a 189a Tertiary-treated wastewater

Lahaina, spring in wastewater plume5 40 19 870b 130b Coastal submarine spring

1

Aravena and others (1993), Cambridge, Ontario, Canada.

2

Honokōhau well, Kona, island of Hawai‘i, present (2009) study.

3

Hunt (2008), Kealakehe, Kona, island of Hawai‘i.

4

Hunt (2007), Kīhei, island of Maui, Hawai‘i.

5

Hunt and Rosa (2009), Lahaina, island of Maui, Hawai‘i.
38

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Figure 27. Graph showing δ18O versus δ15N of nitrate for July 2009 water samples at KalokoHonokōhau National Historical Park, Island of Hawai‘i. Samples plotting up or to the right of other 

samples may reflect addition of isotopically heavier nitrate, or may reflect denitrification or biotic 

uptake from other samples if they plot roughly in the direction of the parallel lines and if their nitrate 

concentration is commensurately less than proposed parent waters (see text).

men14-5078_fig27

Kaloko fishpond

G18 

Honokōhau

well 

NPS tap water 

KAHO 1 

KAHO 2 

KAHO 3 

‘Aimakapā fishpond A45 

MW401

shallow 

MW400 

AP 144 

AP 53H AP 016 

AP 099 

MW401 deep

(December)

-1 

0 

1 

2 

3 

4 

5 

6 

1 2 3 4 5 6 7 8 

δ18O ofdissolved nitrate, in per mil 

δ15N of dissolved nitrate, in per mil 

July 2009 sample

Deep saline groundwater, 

December 2009 

Lines of 1:2 slope (hypothetical denitrification trend) 

Lines of 1:1 slope (hypothetical uptake trend) 

EXPLANATION

Figure 28. Graph showing nitrate versus δ15N of nitrate for July 2009 water samples at 

Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. The highest δ15N value at 

ʻAimakapā Fishpond corresponds with a fairly low nitrate concentration, suggesting it evolved 

at least partly by denitrification rather than addition of isotopically heavier nitrogen.

EXPLANATION

Honokōhau

well 

NPS tap water 

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko fishpond G18 ‘Aimakapā fishpond A45 

MW401 shallow 

MW400 

AP 144 

AP 53H 

AP 016 

MW401 AP 099 

deep

(December) 

0 

50 

100 

150 

200 

250 

0 

1,000 

2,000 

3,000 

4,000 

1 2 3 4 5 6 7 8 

Dissolved nitrate, in micrograms per liter as N

Dissolved nitrate, in micromoles per liter as N

δ15N of dissolved nitrate, in per mil 

July 2009 sample

Deep saline groundwater, December 2009 
Results and Interpretation 39

Here, one can see that the highest δ15N value at ʻAimakapā 

Fishpond corresponds with a low nitrate concentration, supporting a hypothesis that the heavy δ15N composition there has 

evolved at least partly by nitrate removal processes such as 

denitrification and biotic uptake. The fishponds are bottomed 

with mud in which decomposition of organic matter favors 

denitrification under suboxic, chemically reducing conditions.

The rest of the samples have δ15N values less than 5 per 

mil, and none of the samples have high enough δ15N values 

to implicate septic waste nitrate as distinguishable from soil 

nitrate. However this does not mean that some fraction of 

septic nitrate is not present. All other samples have heavier 

δ15N values than the Honokōhau well, and although many 

samples appear to have comparable or lower nitrate than the 

Honokōhau well, this plot does not incorporate the salinity 

mixing line that is required to compare samples of different 

salinities. Where that was done (figs. 21, 22), recall that many 

samples were actually enriched in DIN relative to the uplandsaline groundwater mixing line, indicating addition of nitrogen 

over and above the concentration in background freshwater 

from the Honokōhau well. In order to both enrich samples in 

DIN as in figure 21 and to displace samples plotting to the 

right of the Honokōhau well as in figure 28, nitrogen that is 

isotopically heavier than that at the Honokōhau well would 

need to be added to upland background water.

December samples displayed roughly similar isotopic 

relations as in July, with a few exceptions (fig. 29). Kaloko 

and ʻAimakapā Fishpond samples have shifted to the far 

upper right of the plot, being heavier in both δ15N and δ18O in 

December than in July. Also, the MW401 shallow sample has 

migrated from its former plotted location at the extreme top 

of the graph to a position within the cluster of samples having 

more intermediate compositions. Furthermore, plotting at 

upper right is Kohanaiki irrigation pond, sampled at the shore 

of the open pond. Kohanaiki pond did not appear on the July 

isotope plots because the July sample did not have enough 

nitrate for isotope analysis. The small amount of nitrate it did 

have in December appears to be governed by similar biochemical cycling as in the fishponds, judging from its similar 

plotting position. Phytoplankton and macroalgae were visible 

in the irrigation pond.

The most likely explanation for the December plotting 

positions of the fishpond samples in figure 29 is uptake of 

nitrate by phytoplankton, although denitrification may also 

play a role. Both fishpond samples lie roughly along uptake 

trends from plausible parent waters (KAHO 1 as a parent 

for ʻAimakapā Fishpond; MW400, MW401, and AP 144 as 

possible parents for Kaloko Fishpond), and fishpond nitrate 

concentrations are much lower than any of these waters (fig. 30,

table 4). The more moderate plotting position of the MW401 

shallow sample in figure 29 likely resulted from the decline in 

DIN concentration from 3,660 to 2,010 μg/L since July, so that 

in December its isotopic composition was more reflective of 

nitrate in natural groundwater and less reflective of the fertilizer nitrate that was prominent there in July.

These arguments are strengthened by figure 30, 

which plots nitrate concentration against δ15N of nitrate for 

December. The heaviest δ15N values at ʻAimakapā and Kaloko 

Fishponds clearly corresponded with low nitrate concentrations. Because the fishponds are largely supplied by groundwater having a composition like that of the nearby anchialine 

pools and monitoring wells, strong nitrogen removal processes 

such as biotic uptake and denitrification are necessary to have 

depleted the fishpond waters of nitrogen to the extent seen in 

figure 30. Kohanaiki irrigation water nitrate concentration was 

expected to be low because the water has undergone reverse 

osmosis desalination, which removes much of the nitrate 

as well as salts. The MW401 shallow sample plots close to 

MW400 in figure 30, reflecting both a December nitrate concentration and δ15N composition at MW401 that probably are 

more in line with local groundwater and less affected by the 

July fertilizer contamination.

Change plots (figs. 31, 32) show that isotope compositions of nitrate were relatively stable at most monitoring 

wells and anchialine pools from July to December. The most 

conspicuous changes were in the two fishponds, where both 

δ15N and δ18O were heavier in the December samples than 

in the July samples. There was a slightly different emphasis 

in isotope changes in each pond. Kaloko Fishpond showed 

the greater increase in δ15N from July to December (fig. 31), 

whereas ʻAimakapā Fishpond showed the greater increase 

in δ18O (fig. 32). The plot for monitoring well MW401 also 

stands out at the far right of figure 32, reflecting the much 

heavier δ18O composition of nitrate there in July as a result of 

fertilizer contamination.

In summary, nitrate stable isotopes showed systematic 

relations within the dataset, with strong evidence that isotopic compositions are modified by biochemical cycling in 

the fishponds. The heaviest δ15N values corresponded to low 

nitrate concentrations in the fishponds and likely resulted from 

nitrogen removal by biotic uptake and denitrification. Heavy 

δ18O at MW401 in July is consistent with a fertilizer source of 

nitrate and the high July DIN concentration there.

Remaining samples had δ15N values that lie within 

the range of natural soil nitrogen and do not compellingly 

implicate septic nitrogen solely by their magnitude. However, 

many of these samples were enriched in DIN and PO4 (plotting above their respective background mixing lines) and had 

δ15N values of +3 to +5 per mil that were slightly heavier than 

the +2 per mil at the upland Honokōhau well. These facts may 

indicate that many of the samples contain some fraction of 

septic effluent.

Alternately, at least for nitrogen, the addition of isotopically heavier nitrate could originate from other sources lower 

on the volcano flank than the Honokōhau well, possibly as a 

result of elevation gradients in rainfall and vegetation. In arid 

parts of Hawai‘i such as at low elevations in the Kona area, 

nitrogen-fixing dryland scrub trees Prosopis pallida (kiawe 

or mesquite) and Leucaena leucocephala (koa haole or lead 

tree) are prolific and contribute nitrate to groundwater (Kay 

and others, 1977; Brock and others, 1987). Wheeler and others 

(2007) measured soil nitrogen δ15N values of +5.4 to +6.4 per 

mil beneath Prosopis velutina stands in Arizona, notably 

heavier than the +2 per mil at the Honokōhau well.
40

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Figure 29. Graph showing δ18O versus δ15N of nitrate for December 2009 water samples at 

Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Kaloko and ʻAimakapā Fishponds 

plots have shifted far to the upper right from their July plotting positions, likely as a result of biotic 

uptake of nitrogen and denitrification.

men14-5078_fig29

KAHO 1 

KAHO 2 KAHO 3 

Kaloko

fishpond G18 

‘Aimakapā

fishpond A45 

Irrigation pond 

MW401

shallow 

MW401

deep 

MW400 

AP 144 

AP 016 AP 53H 

AP 099 

Honokōhau

well (July) 

1 2 3 4 5 6 7 8

δ18O of dissolved nitrate, in per mil 

δ15N of dissolved nitrate, in per mil 

December 2009 sample

Upland groundwater, July 2009 

Lines of 1:2 slope (hypothetical denitrification trend) 

Lines of 1:1 slope (hypothetical uptake trend) 

EXPLANATION

6

5

4

3

2

1

0

-1

Figure 30. Graph showing nitrate versus δ15N of nitrate for December 2009 water samples 

at Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Heaviest δ15N values in 

Kaloko and ʻAimakapā Fishponds correspond to low nitrate concentrations, suggesting they 

evolved by biotic uptake of nitrogen and denitrification.

KAHO 2 KAHO 1 

KAHO 3 

Kaloko

fishpond

G18 

‘Aimakapā

fishpond

A45 

Irrigation

pond 

MW401 shallow 

MW401 deep 

MW400 

AP 144 

AP 53H 

AP 016 

AP 099 

Honokōhau well

(July) 

0 

50 

100 

150 

200 

250 

0 

1,000 

2,000 

3,000 

4,000 

1 2 3 4 5 6 7 8 

Dissolved nitrate, in micromoles per liter as N

Dissolved nitrate, in micrograms per liter as N

δ15N of dissolved nitrate, in per mil 

December 2009 sample

Upland groundwater, July 2009 

EXPLANATION
Results and Interpretation 41

Figure 31. Graph showing change in δ15N of nitrate from July to December 2009 at 

Kaloko-Honokōhau National Historical Park, Island of Hawai‘i. Kaloko and ʻAimakapā 

Fishpond δ15N values were much heavier in December, likely as a result of biotic uptake 

of nitrogen and denitrification.

men14-5078_fig31

KAHO 1 

KAHO 2 

Kaloko fishpond G18 

‘Aimakapā fishpond A45 

Irrigation pond 

MW401 shallow 

MW400 

AP 144 

AP 53H 

AP 016 

3 

4 

5 

6 

7 

8 

3 4 5 6 7 8 

δ15N in December 2009, in per mil 

δ15N in July 2009, in per mil 

Heavier in December 

Heavier in July 

Line of 1:1 slope (no change) 

Figure 32. Graph showing change in δ18O of nitrate from July to December 2009 at Kaloko-Honokōhau 

National Historical Park, Island of Hawai‘i. Kaloko and ʻAimakapā Fishpond δ18O values were higher in 

December, likely as a result of biotic uptake of nitrogen and denitrification. MW401 had much heavier δ18O 

in July, reflecting the composition of nitrate fertilizer contamination there at the time.

KAHO 1 

KAHO 2 

KAHO 3 

Kaloko fishpond G18 

‘Aimakapā fishpond A45 

MW401 shallow 

MW400 

AP 144 

AP 53H AP 016 

AP 099 

0 

1 

2 

3 

4 

5 

6 

0 1 2 3 4 5 6 

δ18O in December 2009, in per mil 

δ18O in July 2009, in per mil 

Heavier in December 

Heavier in July 

Line of 1:1 slope (no change) 
42

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

Another possible source of isotopically heavier nitrogen 

is direct atmospheric deposition of vehicular exhaust from 

traffic, which has been shown to impart heavier δ15N values to 

vegetation and water near roadways, as compared to natural 

or non-impacted conditions (Redling and others, 2013). For 

example, Pearson and others (2000) found that mosses collected near highways or busy urban roads had δ15N values 

ranging from -1 to +6 per mil, whereas those collected in rural 

areas with little traffic had values ranging from -12 to -2 per 

mil. Using pine needles, Ammann and others (1999) measured 

δ15N values about +2 per mil heavier near roadways than away 

from roads, and Kenkel and others (2013) measured a smaller 

offset of +1 per mil close to roads.

The Kona area has a dense network of roads in the 

various residential commercial developments and two main 

highways running parallel to the coast, one in the lowlands 

(Queen Ka‘ahumanu Highway) that borders the inland edge of 

the Park. Further research and a greater number of mid-slope 

groundwater samples would be required to evaluate the effects 

of nitrogen-fixing vegetation and vehicular emissions on 

groundwater nitrogen and nitrate isotopic compositions in the 

vicinity of the Park.

Stable Isotopes of Boron

Boron isotopes did not work well as a wastewater tracer 

at KAHO. Only a few water samples were analyzed for boron 

isotopes at KAHO because it was anticipated that the brackish 

salinity of most waters would simply result in a seawater isotopic signature. This proved to be true for three groundwater 

samples from within the Park that were analyzed (KAHO 1, 

KAHO 2, and KAHO 3; table 3), all of which had δ11B compositions very close to a seawater δ11B composition of about 

+39.5 to +40 per mil (Widory and others, 2005; Thomas D. 

Bullen, USGS Boron Isotope Lab, oral commun., 2005).

Wastewater commonly has a light boron isotope composition imparted by laundry detergents that contain sodium 

perborate, a fabric whitening agent having a δ11B composition of about 0 per mil (Vengosh and others, 1994; Thomas 

D. Bullen, USGS Boron Isotope Lab, oral commun., 2005). 

At Kīhei, Maui, a wastewater boron signature was detected 

successfully, being isotopically lighter than ambient groundwater (Hunt, 2007). Municipal wastewater at Kīhei had δ11B = 

+32 per mil, presumably from detergent boron with δ11B = 0 

having been added to household tap water with δ11B = +48 per 

mil in the course of doing laundry. The intermediate δ11B value 

of +32 per mil in wastewater contrasted strongly with the 

local groundwater δ11B of +49 per mil, thereby making boron 

isotopes a good wastewater tracer at Kīhei. Indeed, a water 

sample from a lowland well within the injected wastewater 

plume had a δ11B value of +30 per mil, confirming the presence of wastewater in the aquifer (along with other confirmatory constituents). However, in terms of concentration, 

Kīhei wastewater contained only 195 μg /L of boron, whereas 

seawater contains roughly 4,400 μg /kg of boron (QuinbyHunt and Turekian, 1983), or 4,300 μg/L due to the density 

difference of seawater versus freshwater (1.025 versus 1.000). 

In a coastal aquifer, groundwater containing more than about 

15–20 percent saltwater will have a boron content dominated 

by seawater boron, which will greatly mask lesser boron contributions from other sources and force the isotopic signature 

to very near the seawater value of δ11B = +39 to +40 per mil.

This situation appears to be true at KAHO. Boron-isotope 

values at KAHO 1, KAHO 2, and KAHO 3 were all very close 

to +40 per mil and the samples ranged from 16 to 33 percent 

seawater (table 3). Nearly all of the other pond and anchialine 

pool samples were saltier than 20 percent seawater, and so 

δ11B will not likely be a useful wastewater tracer at KAHO 

because seawater boron will dominate the isotopic signature of 

most park waters.

In addition to the δ11B values from well samples at 

KAHO 1, KAHO 2, and KAHO 3, the δ11B values from the 

Honokōhau well and NPS office tap water were considered. 

These two freshwater sites sampled had δ11B values of about 

+24 per mil, already lighter than the Kīhei wastewater composition and not much different from the +26 value of Kealakehe 

wastewater (Hunt, 2008). Therefore, if these samples are 

generally representative of upland groundwater in the area, 

one will not be able to distinguish a wastewater component 

from the regional fresh groundwater as was apparent at Kīhei, 

where upland groundwater was isotopically heavier than 

wastewater (δ11B = +49 versus +32 per mil). That is, even if 

light or intermediate compositions well under the seawater 

value of +40 per mil were to be detected, it would be impossible to distinguish whether the light composition was signifying 

wastewater or simply isotopically light upland groundwater. A 

wider-ranging survey of upland groundwater will be necessary 

if use of boron isotopes is to be attempted as a wastewater 

tracer in the Kailua-Kona area. Even then, application near the 

coast will be difficult because of the overwhelming effect of 

salinity in greatly masking lighter freshwater δ11B signatures 

to the seawater value.

Apparent Chlorofluorocarbon Age at the 

Honokōhau Well

A chlorofluorocarbon (CFC) groundwater age was determined on a single groundwater sample from the Honokōhau 

well (table 3). Analysis yielded an apparent groundwater age 

of 48–52 years from the 2009 sampling date, or an apparent 

recharge date of 1955–61. The apparent age or date corresponds to the time of last contact with atmospheric air before 

the water became sequestered below the water table. More 

specifically, “last contact” will be with air in pore spaces of 

the unsaturated zone (just above the water table in the aquifer) 

and not air at the land surface, so infiltration time from land 

surface to the water table is not part of the CFC apparent age.

Chlorofluorocarbons are anthropogenic compounds that 

have been released to the atmosphere over decades as a result 

of their use as refrigerants, propellants, solvents, and foamblowing agents. Three CFC compounds (CFC-11, CFC-12, 
Results and Interpretation 43

CFC-113) are used for dating water samples by comparing 

concentrations in the sample with atmospheric concentration histories that have been established for each compound 

(Plummer and Busenberg, 1999).

The Honokōhau well was the only suitable site on which 

to attempt CFC dating because the well is solid-cased to 14 ft 

below the water table, preventing water pumped from below 

the water table from contacting the modern atmosphere or air 

in the unsaturated zone. In contrast, anchialine pools and the 

fishponds are directly exposed to the modern atmosphere, and 

the KAHO monitoring wells have screens or openings that 

extend above the water table. This exposes well water to modern air in the shallow unsaturated zone, and this is exacerbated 

by tidal fluctuations of the water table that entrain modern air 

from the capillary fringe into shallow groundwater on every 

tidal cycle.

The significance of the five-decade old CFC groundwater age at the Honokōhau well is not immediately clear. 

One might expect water from this well to be younger, given 

its location in the high-recharge band on the mountain flank 

where young recharge should be arriving at the water table 

continually. But the long open interval of the well (130 ft long, 

from 14–144 ft below the water table) may allow a substantial 

amount of old water to be drawn from deep in the well, blending in and resulting in a fairly old apparent age. The well may 

also draw some amount of old water flowing laterally from 

higher elevations, water that has been in the aquifer a long 

time during its journey downslope.

Pharmaceuticals, Wastewater 

Compounds, and Volatile Organic 

Compounds

Pharmaceuticals and wastewater compounds at KAHO 

were mostly non-detectable or at low, “trace-level” concentrations below laboratory reporting levels and did not yield 

strong indications of wastewater presence. If wastewater or 

septic leachate is present throughout the study area, it is at no 

more than trace levels, at least as expressed by pharmaceuticals and wastewater compounds analyses on the water samples 

that were collected. Furthermore, no solvents, gasoline compounds, or other VOCs were detected that could be attributed 

to commercial and industrial activities at the industrial park or 

roadside dry wells just upslope from the Park.

All KAHO samples were analyzed for pharmaceuticals 

and wastewater compounds (tables 3, 4) because there are 

known septic systems and cesspools upslope from the Park 

and because of the proven usefulness of these compounds for 

indicating wastewater presence in the environment. Research 

and sampling surveys for these compounds have been conducted internationally and in the United States (for example, 

Kolpin and others, 2002; Glassmeyer and others, 2005; 

Focazio and others, 2008), as well as locally on Maui (Hunt, 

2007; Hunt and Rosa, 2009) and south of KAHO at Kealakehe 

(Hunt, 2008). Volatile organic compounds are another class 

of chemicals that were analyzed for selected sites at KAHO. 

These chemicals include solvents and gasoline hydrocarbons 

that are generally thought of as urban contaminants, for which 

possible sources might include Kaloko Light Industrial Park 

and roadside dry wells immediately upslope from the Park 

(fig. 3; Izuka and others, 2009).

Results for July

In July, wastewater compound analysis detected bromoform (3.6 μg/L) in NPS office tap water, bromoform (0.283 μg/L)

and methyl salicylate (0.1 μg/L) at anchialine pool AP 099, 

and cholesterol (1 μg/L) at Kohanaiki irrigation pond (table 3). 

At AP 099, VOC analysis also detected bromoform at 0.52 μg/L,

providing some support to the bromoform detection on the 

wastewater compounds analysis (the difference in concentrations is not of great concern and may arise from different 

instrument sensitivities and differing degrees of compound 

recovery between the two methods). Neither bromoform nor 

methyl salicylate were detected at AP 099 in December (table 4),

despite being resampled for both the wastewater compounds 

and VOC analyses.

Bromoform is most commonly known as a disinfection 

byproduct of water chlorination. Methyl salicylate is listed as 

being used in liniment, food, beverages, and UV-absorbing 

products such as sunscreens. Cholesterol is a naturally occurring plant and animal sterol; its detection at Kohanaiki irrigation pond may have resulted from plant or animal biota having 

become established in the lined but open pond.

Detection of bromoform in the tap water sample is unsurprising because the tap water is drinking water that has been 

chlorinated, and chlorination is a known means of bromoform 

creation. Bromoform was not detected in the Honokōhau well 

sample, and this is explainable because the sample was drawn 

at the wellhead, prior to tank storage and chlorination for 

distribution through the water-delivery pipeline system. These 

results support a conclusion that bromoform is not present in 

upland groundwater but is instead a chlorination by-product 

introduced in the chlorinated water supply distributed to 

the tap.

Bromoform at anchialine pool AP 099 might originate 

by natural processes or from chlorinated water. Bromoform 

is produced naturally by macroalgae (Nightingale and others, 

1995) and so its presence may be a natural product of algae 

in the anchialine pool itself or in nearby seawater. Chorinated 

water could migrate to AP 099 as groundwater flow from the 

east or by tidal incursion of harbor seawater into the peninsula 

aquifer from north and south. Anchialine pool AP 099 lies 

within a narrow peninsula (fig. 3), with Honokōhau Harbor adjacent to its south side and the ‘Ai‘ōpio Fishtrap and 

beaches to the north. Potential sources of chlorinated water 

in the vicinity include wash-down hoses at boat slips, several 

“wash rack” areas east of the peninsula for boats pulled from 

the water, and several septic systems at harbor restrooms and 

restaurants. Also, the harbor is thought to intercept the treated 

and chlorinated wastewater effluent plume from Kealakehe 
44

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

WWTP, as evidenced by high phosphorus concentrations in 

harbor seawater (Johnson and others, 2008) and tracing of 

the pharmaceutical compounds carbamazepine and sulfamethoxazole in the aquifer from the point of effluent disposal 

to groundwater springs at the back wall of the harbor (Hunt, 

2008). Other potential sources of chlorine include the use of 

bleach and cleaning products in washing down boats, both 

at individual boat slips in the harbor and at on-land wash 

racks. Methyl salicylate at AP 099 may reflect a sunscreen 

or liniment origin, either from direct contact from visitors 

to the Park, or by tidal incursion of ocean water into the 

peninsula aquifer.

Remaining laboratory detections are of low confidence. 

Caffeine was detected at low concentrations below the LT-MDL 

in a number of samples in both the pharmaceuticals and wastewater compounds analyses; however, it was also detected in 

the field blank on the pharmaceuticals method and in both 

the field and laboratory blanks on the wastewater compounds 

method (table 3). Because of the blank detections, the laboratory initially raised the laboratory reporting level (LRL) for 

this data set from the usual 0.06 μg/L to 0.2 μg/L and reported 

all samples as non-detections for caffeine at <0.2 μg/L. This 

effectively “hard-censored” the caffeine results at 0.2 μg/L, 

with no further reporting of values below that. Because one 

will look for concurrence between two methods for a compound that is in both analyses, it became important to equalize 

the reporting style for both analytical schedules (pharmaceuticals and wastewater compounds) and, in fact, the laboratory 

had detected low caffeine concentrations in many samples 

below the LT-MDL prior to hard-censoring at 0.2 μg/L on 

the wastewater compounds analysis. These raw values were 

obtained from the lab to better evaluate potential concurrence 

or non-concurrence of results from the two methods. Now 

having both sets of low-level results available for comparison, 

there was co-detection between the two methods for 6 of 

16 samples (including the field blanks), 5 samples where the 

two methods agreed on non-detection, and 3 samples where 

caffeine was detected on one analysis but not the other.

Recognizing that caffeine concentrations reported for 

the environmental samples are very low (below the LT-MDL) 

and that they are accompanied by detections in blanks, the 

caffeine results should be considered inconclusive. The data 

may contain some true environmental detections originating 

from septic sources upslope or perhaps even a field contamination artifact via pervasive atmospheric deposition from coffee 

roasting facilities (there is at least one roaster in the commercial zone along the main highway between Honokōhau Harbor 

and the landfill; fig. 3). However, this last possibility cannot be 

meaningfully distinguished from the possibility of laboratory 

contamination at such low concentrations.

Other than caffeine, a few other compounds were 

reported below the LT-MDL in July (table 3). Many of the 

detections were in the sample from Kohanaiki irrigation 

pond, which is open to contamination from the environment 

and from workers on the property. The irrigation pond has 

an artificial membrane liner that may explain detections of 

compounds such as plasticizers. Toluene was detected above 

the laboratory reporting level in the VOC field blank but not in 

any environmental samples.

Results for December

There were only two detections above the LT-MDL in 

December (table 4): caffeine in the wastewater compounds 

analysis at both Kaloko Fishpond and Kohanaiki irrigation 

pond. Possible sources include recreational swimmers at 

Kaloko Fishpond, dumping of soft drinks or coffee at both 

sites, and possible atmospheric deposition from coffee roasters 

in nearby commercial zones, as was previously mentioned. 

Caffeine was also detected in field and laboratory blanks, but 

at concentrations roughly one and two orders of magnitude 

lower (lab blank and field blank, respectively) than the environmental concentrations.

At monitoring well KAHO 2, closest to Kaloko Light 

Industrial Park, trace-level concentrations (below the LT-MDL)

were detected on the pharmaceuticals method for carbamazepine (0.001 μg/L), sulfamethoxazole (0.003 μg/L), and 

thiabendazole (0.016 μg/L). Carbamazepine was also detected 

at 0.001 μg/L in anchialine pool AP 099. The three compounds 

were not detected in laboratory blanks, and a field blank was 

not run for pharmaceuticals because only three samples were 

being analyzed in December.

Carbamazepine is an anticonvulsant, sulfamethoxazole 

is an antibiotic, and thiabendazole is a fungicide and 

worming agent. Carbamazepine and sulfamethoxazole are 

very persistent once released to the environment (Drewes and 

others, 2003; Barber and others, 2008) and are commonly 

the only pharmaceuticals detected in some water samples. 

Carbamazepine and sulfamethoxazole were detected in treated 

municipal wastewater and in wells and coastal springs within 

injected wastewater plumes on Maui, although at concentrations one to two orders of magnitude greater than the concentrations at KAHO 2 and AP 099 (Hunt, 2007; Hunt and 

Rosa, 2009). Both compounds were detected south of KAHO 

by Hunt (2008), who sampled Kealakehe treated wastewater, 

two coastal springs at Honokōhau Harbor, and two monitoring wells between the harbor and the Kealakehe wastewater 

disposal pit. Carbamazepine was detected in all samples and 

sulfamethoxazole was detected in all samples except one of 

the two harbor springs. Concentrations decreased progressively from the disposal pit to the harbor, with concentrations 

reaching one to two orders of magnitude greater than the 

concentrations at KAHO 2 and AP 099.

The very low concentrations of carbamazepine, sulfamethoxazole, and thiabendazole reported for the KAHO 2 

sample may represent trace-level detections of septic leachate 

from Kaloko Light Industrial Park and suburban developments 

farther upslope. Carbamazepine at AP 099 could be a tracelevel indication of incursion of harbor seawater, containing a 

slight wastewater fraction into the peninsula aquifer.
Summary and Conclusions 45

Optical Brightener Fluorescence

A screening test for laundry fabric brighteners (optical 

brighteners) gave positive results for many samples (table 5). 

Samples testing positive either in July or December were

• Monitoring wells KAHO 1, KAHO 2, KAHO 3, 

MW401 shallow; 

• ʻAimakapā Fishpond and Kohanaiki irrigation pond; 

and

• Anchialine pools AP 016, AP 53H, AP 144.

Samples testing negative were

• Monitoring wells MW400 and MW401 deep;

• Kaloko Fishpond; and

• Anchialine pool AP 099.

All blanks and controls tested negative, and a replicate 

sample at monitoring well KAHO 1 in December tested positive in the same fashion as the primary sample for KAHO 1.

Samples were screened for optical brighteners using 

UV-fluorescence methods. Meter readings were in arbitrary 

fluorescence units and strictly comparable only within the 

dataset and in relation to control samples of deionized water 

and tap water. Some environmental readings were below zero, 

but not as strongly negative as the control samples, indicating 

“more fluorescence” than the controls (the instrument was not 

reset to a zero value corresponding to the control samples but 

was instead simply left at the factory calibration setting).

Taken at face value, these results would be thought to 

indicate the presence of optical brighteners—presumably 

from laundry graywater—at nearly all sites. While this may 

be the case, it is important to remember that this is simply 

a screening method using fluorescence, which is subject 

to potential interferences such as dissolved organic matter 

(DOM). A more rigorous test for optical brighteners would be 

a gas-chromatograph test for the brightener compounds themselves. To infer the presence of wastewater and (or) graywater 

with confidence, one would also hope to detect pharmaceutical 

or wastewater compounds as supporting evidence.

Fluorescence readings can be equivocal because of 

interference from naturally occurring DOM such as humic 

and fulvic compounds, whose fluorescence spectrum overlaps 

the optical brightener emission band (Chen and others, 2003; 

Turner Designs, 2007b). A familiar example of high-DOM 

water is transparent but highly colored swamp water that 

resembles brownish tea.

Also of potential significance are the relatively low initial 

readings for the KAHO samples in table 5 (the highest reading 

corresponding to a positive result was 4.5 units on the meter). 

This was the same meter used by Hunt (2008) that produced 

readings of 31 for Kealakehe treated wastewater effluent 

and readings of 20 and 23 at two monitoring wells in the 

presumed aquifer wastewater plume between the Kealakehe 

wastewater disposal pit and Honokōhau Harbor. If the much 

lower readings in table 5 are reliable indicators of brightener 

presence, they indicate a much more dilute graywater and (or) 

wastewater fraction than that in the Kealakehe effluent and 

aquifer plume. This is expected, considering that cesspool and 

(or) septic sources of laundry graywater upslope from KAHO 

are widespread and not concentrated in one localized area like 

the Kealakehe wastewater plume. A final factor is that the 5- 

and 10-minute UV illumination steps were not applied to the 

Kealakehe samples, and there is no way to know how much of 

the UV fluorescence readings for those samples was contributed by dissolved organic matter, which could be quite high in 

the municipal effluent.

Summary and Conclusions

Baseline water-quality sampling was conducted for dissolved nutrients, and chemical and stable-isotope tracers at 

Kaloko-Honokōhau National Historical Park on the Island 

of Hawai‘i in July and December 2009. Sites in and near the 

Park included four anchialine pools, two large fishponds, 

five monitoring wells, an upland production well, tap water, 

and a holding pond for golf-course irrigation water. There 

were no significant rainstorms during the sampling period, so 

both samplings were fair-weather snapshots of water quality; 

although intended, it was not possible to obtain a wet-weather 

or storm sample because of the unusual dryness in 2009. Wetweather results could differ from those reported here.

Water samples within the coastal park were brackish, 

ranging in salinity from 15 to 67 percent seawater. The freshest water sampled was from outside of the Park, a reference 

sample of background fresh groundwater from the upland 

Honokōhau production well at an elevation of 1,675 ft above 

sea level. The saltiest water was two-thirds that of seawater 

salinity and was obtained from 45 ft below the water table in 

monitoring well MW401. Temperature and salinity profiles 

measured in that well by NPS indicate that the coastal brackish 

groundwater lens is underlain by cold saline water much different from the warm surface seawater nearby and originating 

from deep within the oceanic thermocline offshore. The cold 

saline groundwater is much higher in nitrogen and phosphorus than surface seawater, and it is important to take this into 

account in water-quality studies at the Park.

Samples were analyzed for dissolved inorganic nutrients (nitrogen and phosphorus), stable isotopes (nitrogen and 

oxygen in dissolved nitrate; hydrogen and oxygen in the water 

molecule; dissolved boron), pharmaceuticals, wastewater compounds, and volatile organic compounds. Samples were also 

screened for the presence of laundry fabric brighteners using 

UV-fluorescence tests.

Highly elevated nitrogen concentrations were detected at 

three sites on the Park’s north boundary and can be attributed 

to fertilizer contamination. Maximum nitrogen concentrations 

at monitoring wells MW401 and MW400, and anchialine pool 

site AP 144 were 280, 111, and 75 percent above expected 

background concentrations along a freshwater-saltwater 
46

Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau

mixing line defined for the area, respectively. These highly 

elevated concentrations likely resulted from fertilizer application during the turf grow-in period of the newly constructed 

golf course at The Shores at Kohanaiki resort. The fertilizer 

influence appears to have been temporary, with the highest 

nitrogen concentration in July falling substantially by December, although not fully back to the expected background level 

for that vicinity.

Aside from this localized fertilizer influence, remaining 

samples had lesser enrichments of nitrogen and phosphorus 

above expected background concentrations (40 percent or less 

above background for nitrogen and 57 percent or less above 

background for phosphorus). The nitrogen and phosphorus 

enrichments at KAHO reflect gains in nutrient concentrations across the intervening landscape between the upland 

Honokōhau well and the coastal lowlands. Potential sources 

for the nutrient enrichment include rock weathering; nitrogen fixation and decomposition of natural vegetation on the 

mountain flank; fertilizers used on suburban, commercial, and 

agricultural lands; septic leachate from suburban and commercial developments; and atmospheric deposition including 

vehicular emissions.

Stable isotopes of nitrate did not implicate septic or waste 

nitrate in the usual way; that is, by conspicuously heavy δ15N 

values of +10 per mil or greater that would tend to exclude a 

natural soil nitrogen source. Most water samples had nitrate 

δ15N values ranging +3 to +5 per mil, heavier than the value of 

+2 in upland background water from the Honokōhau well, but 

still within the range for natural soil nitrate, and therefore not 

strongly indicative of waste nitrogen. Samples with heaviest 

nitrate δ15N values (ranging from +6.2 to +7.7 per mil) were 

from the fishponds, where plants, animals, and microbes drive 

biotic cycling such as phytoplankton uptake of nutrients, 

transformations within the food chain, and denitrification in 

pond-bottom sediments. Despite the lack of a conspicuous 

waste nitrogen isotopic signature, groundwater samples with 

δ15N values of +3 to +5 per mil were still isotopically heavier 

than the +2 per mil in upland groundwater at the Honokōhau 

well. This isotopic enrichment could reflect a fraction of septic 

nitrate in the samples or some other unknown variation in 

nitrate isotopic composition on the mountain flank, for example spatial variation of nitrogen-fixing plants such as Prosopis 

pallida (kiawe or mesquite) and Leucaena leucocephala (koa 

haole or lead tree). Vehicular emissions could also be a source 

of isotopically heavier nitrogen across the watershed, as studies have shown heavier δ15N values in plants and soil next to 

busy roadways than at control sites farther from roads.

Some fraction of septic leachate is expected in KAHO 

groundwater given the extensive residential and commercial 

developments upslope that are on septic systems and cesspools. Evidence for detection of septic leachate was greatest at monitoring wells KAHO 1 and KAHO 2 (closest to 

Kaloko Light Industrial Park) and included enrichment of 

nitrogen and phosphorus above expected background concentrations, heavier δ15N values than background, detection 

of hydrogen sulfide by smell (KAHO 1), and detection of 

the pharmaceuticals carbamazepine, sulfamethoxazole, and 

thiobendazole (KAHO 2) at trace-level, parts-per-trillion 

concentrations.

If septic contamination is present generally in park 

waters, it appears to be at a subtle level that is not conspicuous 

in most samples. Pharmaceuticals, wastewater compounds, 

and volatile organic compounds did not indicate strong septic 

or other contamination in park waters; only a few compounds 

were detected and most of these at trace-level concentrations. 

A screening-level test for laundry fabric brighteners indicated 

positive detection at most sites. However, initial readings were 

quite low compared to prior experience with municipal wastewater plumes, and the method is subject to interference from 

natural humic and fulvic compounds. If laundry graywater is 

present in most of the samples that tested positive, it may be a 

small, dilute fraction.

One possible explanation for the apparent lack of strong 

wastewater and graywater indicators is that cesspool and septic sources are widespread and leach at low individual rates, 

approximating a diffuse nonpoint source or a widespread distribution of small point sources. This is a very different setting 

than the concentrated municipal wastewater injection plumes 

previously studied, where chemical and isotopic evidence of 

wastewater presence in wells and springs was apparent on 

Maui (Hunt, 2007; Hunt and Rosa, 2009) and south of the 

Park at Kealakehe (Hunt, 2008).

No solvents, gasoline compounds, or other VOCs were 

detected that could be attributed to commercial and industrial 

activities at Kaloko Light Industrial Park or to roadside dry 

wells in and uphill from the Park. Bromoform and methyl 

salicylate were detected at anchialine pool AP 099, possibly 

indicating the presence of chlorinated water (bromoform) and 

liniment or sunscreen (methyl salicylate). These detections 

may have originated directly, from human activity at the 

anchialine pool; or possibly indirectly, by incursion of surface 

seawater into the narrow peninsula from Honokōhau Harbor to 

the south or from the ‘Ai‘ōpio Fishtrap, its adjacent beach to 

the north.

Study Limitations and 

Opportunities for Future 

Research

Results of this study provide a reasonable baseline of 

nutrients and wastewater tracers for future comparison. A 

serious limitation to the study is that a wet-weather or storm 

sampling was not obtainable because the study period was 

unusually dry. Another limitation is that—in order to make 

best use of available funding—not all sites were sampled 

twice, and some of the more expensive laboratory analyses 

were not applied at all sites, but only at sites where it was presumed they were more likely to yield definitive results.

Repeat monitoring would need to employ some of the 

same methods for comparability, but it may be sensible to drop 
References Cited 47

some methods or shift financial resources to other methods 

that may prove more productive. Simple dissolved species 

of inorganic nutrients were analyzed and were sufficient to 

document a general nutrient enrichment above background in 

many samples, and acute but temporary effects of fertilizer 

leaching at sites along the north boundary of the Park. Nutrient 

results also appear to reflect the influence of biotic cycling in 

the larger fishponds; however, organic and particulate nutrient 

forms would need to be analyzed for further understanding of 

biotic nutrient cycling within park waters. Similarly, organic 

nutrient species and dissolved organic carbon could be useful constituents to measure for more complete monitoring of 

septic influences.

Stable isotopes of nitrate did not give strong indications 

of septic nitrogen directly, but did reflect a general pattern of 

heavier isotopic values in the lowlands as well as the likely 

influence of biotic nitrogen cycling in the larger fishponds 

where δ15N values were heaviest. All groundwater samples 

were isotopically heavier than upland groundwater at the 

Honokōhau well; this reflects some addition of heavier nitrate 

in the samples, either from septic sources, from nitrogenfixing vegetation, or from atmospheric deposition of vehicular exhaust. This topic could be pursued by an experienced 

isotope geochemist who might also apply additional measurements such as stable isotopes of phosphorus, carbon, and 

sulfur. A critical need would be samples from some “midslope” wells; that is, between the coastal lowlands and park 

environs and Māmalahoa Highway where the Honokōhau well 

is located.

VOCs were analyzed mainly as an initial screening tool 

for sites closest to Kaloko Light Industrial Park. Given the 

general lack of detections on that method, one might drop 

it in future sampling in favor of more widespread sampling 

for pharmaceuticals and wastewater compounds. Alternately, 

VOCs might be retained but only for a few sentry sites such 

as KAHO 1 and KAHO 2 that are closest to Kaloko Light 

Industrial Park.

Even in the pharmaceutical and wastewater compound 

analyses there were few detections, and one might question 

the cost-effectiveness of continuing to monitor for these compounds. However, that perspective doesn’t address the possibility of contaminants from roadside dry wells and cesspools 

in Kaloko Light Industrial Park and elsewhere being flushed 

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rainstorms. Storm-sampling strategies considered during this 

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The screening test for laundry fabric brighteners is a very 

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fluorometer. More definitive testing might be attempted using 

laboratory-grade fluorescence spectroscopy, and this would 

best be done by an expert in the methodology with experience 

in wastewaters and fabric brightener fluorescence in particular.

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37 p.
Menlo Park Publishing Service Center, California

Manuscript approved for publication August 15, 2014

Edited by Larry Slack and Kate Jacques

Design and layout by James E. Banton
Hunt—Baseline Water-Quality Sampling to Infer Nutrient and Contaminant Sources at Kaloko-Honokōhau—Scientific Investigations Report 2014–5158

ISSN 2328-0328 (online)

http://dx.doi.org/10.3133/sir20145158