Kawa Stream TMDL Project
Stream Assessment Report

AECOS Inc. & Oceanit

Introduction
Under Section 303(d) of the Clean Water Act, The Environmental Protection Agency (EPA) requires that each state develop a list of waters1 that fail to meet established water quality standards. These listed waters are regularly prioritized and higher priority waters given closer scrutiny under that state's Total Maximum Daily Load (TMDL) program. A TMDL specifies the maximum amount of a pollutant that a water body can receive and still meet water quality standards, and a TMDL allocates pollutant loadings among point and nonpoint pollutant sources. In order to accomplish a TMDL for any particular water, a study of that water body must be completed. Kawa Stream in Kane`ohe was selected in 1999 for such a study, in part because pollutants carried in stream discharges have an impact upon nearshore marine waters. Kawa Stream empties directly into the southern part of Kane`ohe Bay, a water body designated Class "AA" and, in the area receiving discharges from both Kawa and Kane`ohe streams, a State designated water quality limited segment (WQLS). That is, a marine coastal environment that does not meet the water quality standards for the class designation. Kawa Stream was selected initially because its small size and location within an urban watershed on the wetter windward side of the Island of O`ahu suggested that studies to be conducted later on larger, more complex drainage systems could benefit from methodologies developed for the Kawa Stream TMDL. A TMDL study is now underway for nearby Kane`ohe Stream.

Kawa Stream, like most Hawaiian perennial streams, is characterized by periods of relatively steady, base flow and short periods of high flow (termed freshets) resulting from heavy rains on the watershed. Physical and chemical properties of the water can vary between these two types of flow, as well as between storms of different magnitudes and at different times during storm flow. The study approach requires making water quality measurements at locations which permit attribution of substances carried in the flow to sources in the watershed. Historical and ongoing water quality monitoring are used to indicate which parameters are out of compliance with their respective water quality standards. This reliance on monitoring, independent of events such as storms, is necessary because the water quality standards promulgated by the State of Hawaii, Department of Health (DOH) are frequency-based for most water quality characteristics. Single measurements cannot be used to establish compliance, except for certain toxic substances (see HAR 11-54-04, acute toxicity standards). Ideally, monitoring should distribute samples across wet and dry seasons (for which different criteria may apply), and be unbiased with respect to water quality influencing events occurring in the watershed.

For Hawai`i this means that two different types of samples must be collected to complete a TMDL study: (1) samples that are collected independent of events, and (2) samples that are representative of runoff events (the freshets). The former may come from an existing data base, since the primary purpose is to characterize water quality in the stream in relation to the water quality standards and establish which parameters are not in compliance, requiring establishment of a TMDL. The latter cannot be used in a data base the purpose of which is to establish compliance with water quality standards. With respect to certain parameters at least, especially those related to suspended particulates (turbidity and TSS, for example), samples collected purposely to characterize a freshet would not be expected to comply with our standards. These samples are considered tainted or biased, but are useful as inputs to watershed models developed to explain the relationship between rainfall and stream pollutants.

This report presents summaries and discussions of data pertinent to the development of a TMDL for Kawa Stream. The actual (draft) TMDL for Kawa Stream can be downloaded as a .pdf document from the HDOH, Environmental Planning Office (EPO) website. Presentation of our data summaries and pertinent discussions as a set of Internet (WWW) topic pages provides for easy and rapid dissemination of gathered information, including raw water quality and other data. Because a TMDL is ultimately a public process, this approach is intended to promote public knowledge and interest. Further, as a hypertext document, the Internet report can have a web-structure rather than the printed TMDL's linear structure. Topics can be presented as internally consistent pages that can be read (or skipped) in whatever order the user chooses based upon interest. Data may appear as summary tables or graphs on these pages, linked to the raw data tables. Following are links to these topic pages:

PROJECT PAGES:  at AECOS / at OCEANIT
Rainfall & Stream Flow Watershed Influences Kawa Stream WQ Kawa Estuary WQ
Discussion

Data Sources

Historical data for Kawa Stream includes monitoring at several locations in the lower part of the watershed in 1991-92 and 1996. A one year effort (September 1999 through September 2000) of monitoring by the State HDOH included stations ranging from the mouth of Kawa Stream, through the estuary, and upstream to just above the residential district. In this program, samples were collected twice a month on predetermined dates (i.e., sampling was not biased with respect to events, such as rain storms). Thus, these samples define the general water quality conditions in this stream system. 3 The laboratory results are presented in HDOH Data and data summaries are given in HDOH Data statistics and in various tables included with the discussion that follows.


Page Footnotes:
1 -- EPA's list of impaired waters for Hawai`i (1998). A more up to date discussion provided by DOH can be found in the report Clean Water Branch, Excerpts from 2000 305(b) Report (May 12, 2000). For a discussion of the TMDL process nationwide start with the National Academy of Sciences report.
2 -- Kawa Stream "reaches" are defined elsewhere.
3 -- It was learned after completion of the draft TMDL for Kawa Stream that the HDOH laboratory, while reporting total nitrogen (TN) and total phosphorus (TP) values for Kawa Stream samples, was filtering samples before the digestion step required by the analytical procedure. Filtering removes all particulates larger than a certain size (the "pore" size of the filter), and therefore the results obtained on filtered samples do not represent all of the nitrogen and phosphorus present. Results from filtered samples must be reported as total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP).


Monitoring by the State DOH

The State of Hawaii Department of Health (DOH) conducted twice monthly sampling at 8 or 9 locations (the stream is intermittent at the uppermost stations) on Kawa Stream between September 1999 and September 2000 (25 events). Water quality results from regular monitoring at these stations are posted. DOH sampling locations are as follows:

    Station 1 - Kane`ohe Bay at mouth of Kawa Stream (ELR)
    Station 2 - Kawa Stream estuary in mangrove upstream of mouth (ELR)
    Station 3 - Kawa Stream estuary upstream of Waikalua-Loko (ELR)
    Station 4 - Kawa Stream estuary at Bayview, lower golf cart bridge (ELR)
    Station 5 - Kawa Stream at Bayview, upper golf cart bridge (LR)
    Station 6 - Middle east branch of Kawa Stream down from Mokulele Street bridge (UMR)
    Station 7 - Kawa Stream just upstream of Namoku Street bridge (UMR)
    Station 8 - Upper west branch of Kawa Stream above Parkway Community Center (UMR)
    Station 8(II) - Central branch of Kawa Stream above Parkway Community Center (UMR)
    Station 9 - Kawa Stream above new culvert at Hawaiian Memorial Park (IUR)
    Station 10 - Kawa Stream above confluence with upper west branch (UMR)
Codes in parentheses indicate the stream reach of each station as defined in the description of Kawa Stream. Note that no samples were ever collected at Stations 9 and 10 where Kawa is intermittently flowing. For this reason, in HDOH records, Station 8(II) is sometimes listed as Station 10.


January 23, 2002 — Webmaster
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