Kawa Stream TMDL Project

Discussion towards developing TMDLs for Kawa Stream

WQ Standards Natural Sources
  Water Quality Standards

Hawaii's water quality standards are contained in Chapter 54 of Title 11 of the Hawaii Administrative Rules. The standards are also reproduced on each of the parameter discussion pages linked in the discussion below. In our discussion, measurements made regularly as part of a monitoring program with minimal bias to conditions influencing stream flow (i.e., the HDOH 1999-2000 monitoring program) are used to assess compliance with the standards. Measurements made on an irregular basis (AECOS storm water monitoring) with particular emphasis on rainy periods cannot be used for compliance assessment purposes, but contribute to our understanding of where and how pollutants reach Kawa Stream.

Natural Sources

The parameters of specific interest for Kawa Stream are nutrients and particulates because they are not in compliance with State water quality criteria in at least some parts of the stream system. Once existing water quality in Kawa Stream is understood spatially, the next step in the TMDL process is to ascertain where in the watershed pollutants are arising. The uppermost branches of the system drain undeveloped lands regarded as natural sources and the output of particulates and nutrients from these lands might be defined as background. Unfortunately, those segments of Kawa Stream that drain only forested lands are intermittent. We do not have any direct means of monitoring water quality on a regular basis as required to establish average conditions or assess compliance or non-compliance with State water quality standards. Nor do we have wells within the forest to monitor ground water properties as a baseline to assess inputs from lands of other uses.

In the absence of site-specific values, the quality of water in the "natural" area of the Kawa watershed basins must be estimated. One approach is to consider values measured within or at the edge of the forest in other areas of the State. A second approach is to assume that the water quality criteria in the State of Hawaii, WQS represent conditions characteristic of an undisturbed watershed. Table 1 presents high level ground water means for National Water Quality Assessment (NAWQA) program data collected all around the United States. Table 2 presents stream water quality measurements at stations above significant anthropogenic influences.

Table 1. Geometric mean values for nutrients from U.S. shallow ground water sites (NAWQA water-quality data collected 1992-1996). Units are ug-N/L and ug-P/L.

Land Use NH3
forest 25 (39) 217 (31) 517 (6) 30 (15)
agriculture 36 (753) 3313 (772) 3739 (228) 42 (547)
urban 63 (232) 1900 (216) 2399 (92) 54 (158)

Number of data points given in parentheses

Table 2. Geometric mean values for nutrients from windward Hawaiian streams, samples collected above anthropogenic influences. Units are ug-N/L and ug-P/L; DIN (dissolved inorganic nitrogen) includes ammonia, nitrate, and nitrite.

Stream Name Elev. (m)
Data Source
Kilauea, Windward Kaua`i 90 11 (2) 138 (2) 149 (2) 52 (2) AECOS
Waihe`e, Windward O`ahu 52 85 (9) 92 (14) 177 (9) 47 (9) USGS
Pahe`he`e, Hamakua Hawai`i 400 8 (2) 97 (2) 105 (2) 6 (2) AECOS
Kolekole, Hamakua Hawai`i var. 72 (2) < 1 (2) < 1 (2) 5 (2) AECOS

Number of data points given in parentheses