Assessing waterbody impairment in relation to known pollution sources
Neil Rhoads and Mailea Miller-Pierce, PhD
We are the authors of a scientific paper examining the negative effects of On Site Disposal Systems (OSDS) on marine recreational waters around Maui, specifically, microbial contamination due to human waste. Our paper is currently in preparation for publication and we anticipate it will be accepted for publication in the near future. Our preliminary, summarized results are as follows:
- Our study uses water quality data collected and analyzed by the HIDOH, Clean Water Branch. There were 79 collection sites around Maui which were sampled from 1989 to present. Overall, there were more than 16,000 samples analyzed.
- Of the 79 collection sites, 30 had sufficient sampling to permit analysis of trends over time. Fecal Indicator Bacteria (FIB) concentrations at 27 out of the 30 sites were significantly higher in the years 2004-2016 compared to 1989-1998. Sites with the largest increases in FIB (enterococci concentrations) were: Olowalu (943%), Kanaha Beach (443%), Launiupoko (352%), and Hanaka`o`o (315%).
- Launiupoko is of particular interest because during the study period the adjoining land transitioned from sugar cane production to residential estates employing OSDS. As of 2010, there were 246 OSDSs upslope near Launiupoko, discharging 392,900 gal/day. While the land was used for sugar cane, 94% of sample sets were in the least impaired category of water quality. After installation of OSDS, only 36% of sample sets were in that category. Furthermore, Launiupoko FIB contamination levels are on an upward trend and have increased significantly from 2004 to 2016.
- Our study does not provide a direct causal relationship between OSDS and FIB contamination. However, taking into consideration other studies conducted on Maui and Hawai`i Island, it is reasonable to infer that the proliferation of OSDS near Launiupoko may be the cause of the increased FIB contamination, pending confirmation from further studies.
- The rapid degradation of water quality at Launiupoko demonstrates the importance of monitoring nearshore waters before, during, and after land development involving substantial OSDS effluent.
- Three Kihei collection sites were located within the effluent plume of the Kihei WWRF; Kalama Beach, Cove Park, and Kama`ole Beach #1. Most perfringins impairments in South Maui occurred during 1989-1998, and some instances had very high concentrations (>100 CFU/100 ml) including Kalama Beach.
- There are multiple sites of concern along Mauiâ€™s north shore. The Makawao-Haiku districts in Maui had the highest density of Class IV cesspools (111 units/mi2), and their proximity to shallow groundwater suggests faulty cesspool systems could be a source of FIB contamination. Studies should determine whether any connections exist between Class IV cesspools and coastal water bodies in this region.
- A FIB sample with a concentration high enough to confirm sewage related pollution, was collected at the Maliko Bay site in 2012 and the site was listed as impaired by the HIDOH. This instance, along with the high percentage of WQ exceedances and high volumes of discharged effluent, indicate faulty and leaking cesspool systems within the Maliko Bay watershed.