An investigation was conducted to develop a simple method for tracking the fate and transport of recycled water following recharge into a shallow brackish aquifer ͑caprock aquifer͒ in a coastal area on the Island of Oahu, Hawaii. Several naturally present chemical constituents including the boron isotopic signature ͑␦ 11 B͒ were used to characterize each of the caprock aquifer source waters and the recycled water. Because of the influence of seawater, only ␦ 11 B could be used to clearly distinguish the recycled water from the source waters and the caprock aquifer water. Estimates of the mixing ratios of source waters in the aquifer were made and a method was developed to determine the fraction of wastewater present in a brackish water sample recovered from a monitoring well during recharge operations without addition of a tracer. This method can be adapted to monitor any other brackish aquifer subjected to wastewater recharge.
A survey water quality study was conducted between 2014 and 2017 to investigate the presence and concentration of pesticides in the nearshore marine environments on the islands of Oahu and Kauai. On Kauai, a total of 32 surface water and 16 sediment samples were collected from four streams and one irrigation ditch over multiple sampling events. On Oahu, a total of 27 surface water and 16 sediment samples were collected from six streams on the leeward side of the island over multiple sampling events, typically under baseflow conditions. The samples were analysed for 197 compounds spanning eight chemical classes of pesticides. Five herbicide (glyphosate, metolachlor, atrazine, imazapyr and MCPA) and one insecticide (imidacloprid) compounds were detected in the surface water samples collected. Seven insecticide (imidacloprid, carbaryl, chlordane, p,pʹ-DDD, p,pʹ-DDE, p,pʹ-DDT and dieldrin), five herbicide [glyphosate, aminomethylphosphonic acid (AMPA), diuron, DCPMU and pendimethalin] and one fungicide (azoxystrobin) compound were detected in the stream bed sediments collected. Detected pesticides spanned the pesticide class list, with seven of the eight classes of pesticides tested discovered. This study found widespread, low level contamination by both legacy and currently used pesticides in nearshore waters and river bed sediments on the islands of Oahu and Kauai. Based on the pesticide data obtained during the study, five streams on the island of Oahu (two leeward and three windward streams) were selected for additional high-frequency sampling for the broad-spectrum herbicide glyphosate (Roundup), due to this compound's prevalence and the elevated concentration levels (compared to other pesticides) measured. These five streams flow through watersheds dominated by agricultural, residential and mixed-use land use and were sampled under both baseflow and storm conditions. The pervasiveness and overall concentration levels of glyphosate detected are greater than any other pesticide currently or historically present in Hawaiian streams. Glyphosate was detected in 95% of stream samples collected during storm events (59 samples, 798 ng/L median, 1,308 ng/L mean detects) and 60% of stream samples collected under baseflow conditions (103 samples, 152 ng/L median, 462 ng/L mean detects), respectively (detection limit = 50 ng/L). In addition, either glyphosate or its degradation product AMPA was detected in 100% of the stream bed sediment samples collected on Oahu and Kauai during the study. The higher glyphosate concentrations in measured stream samples collected under storm versus baseflow conditions is believed to result from the release of adsorbed glyphosate present in stream-bed sediments as they become re-suspended during the rapid rises in stream volumes that characterize Hawaiian stream during runoff events. The mean glyphosate concentration measured in streams that drain urban and mixed-use areas (1,020 and 1,050 ng/L, respectively) was slightly higher than concentration levels measured in streams that drain agric...
High-frequency sampling and analysis was conducted for the broad-spectrum herbicide glyphosate (Roundup) in ephemeral and perennial streams receiving storm water runoff generated within agricultural, urban and mixed-used watersheds on the island of Oahu, Hawaii. Glyphosate was selected for analysis since it is the most widely used herbicide in the world, and as a result, tends to be ubiquitous in the environment and our food supply. Samples were collected under both baseflow and storm conditions from five streams. The pervasiveness and maximum concentration levels of glyphosate detected in these streams are greater than any other pesticide currently present in Hawaiian streams. Glyphosate was detected in 96% and 65% of the stream samples collected during storm events (53 samples) and under baseflow conditions (34 samples), respectively (detection limit = 0.05 µg/L). The mean glyphosate concentrations measured in stream samples collected under storm conditions were between five to fifty times higher than mean glyphosate levels measured in the same stream under groundwater dominant baseflow conditions. The highest glyphosate concentrations were measured during a small runoff event in Manoa stream which flows through residential communities in urban Honolulu. The mass of dissolved phase glyphosate measured in stream water during the individual storm events monitored ranged from 0.5 to 18 grams. Between 11% and 23% of the total glyphosate load was present in suspended sediment during three sampled storm events in Honouliuli, Waimanalo and Kawa streams. The estimated total mass of dissolved phase glyphosate that discharged into Kaneohe Bay from Kawa Stream over a four-month monitoring period from December 2017 to March 2018 was 987 grams, with 92% of the pesticide load entering under storm conditions.
The island of Kaua'i is the oldest of the main Hawaiian Islands and has roughly 70,000 inhabitants. Sugar plantations historically dominated the island's economy but have been largely supplanted by tourism in recent years. The surface water resources in the Waimea River watershed on Kaua'i were diverted at the beginning of the twentieth century by former sugar plantations into roughly 77 kilometers of transmission ditches, tunnels, flumes, and siphons of the Kekaha Ditch Irrigation System (KEDIS) and the Kōke'e Ditch Irrigation System (KODIS). These ditch systems were constructed to transport water to the arid, fertile lands of the Mānā Plain that required irrigation water to grow sugarcane. A 2013 petition by community groups to the State of Hawai'i Commission on Water Resource Management (CWRM) demanded that stream flow be restored and that interim instream flow standards for the Waimea River and its headwater and tributaries be established. The current amount of water diverted into the two ditch systems exceeds present-day agricultural needs, which are dominated by corn seed crops. However, the island's electric utility has developed plans to use the water stored in the existing high elevation reservoirs on KODIS to produce electricity using pumped hydropower storage technology. Pumped hydropower would allow the utility to "store" excess energy produced by the island's rapidly expanding utility-scale photovoltaic array systems with the ultimate goal of producing all of the island's electricity using renewable resources. The physical condition and volume of water currently diverted by both ditch systems was evaluated and measured by Element Environmental (E2). CWRM is using the information collected to establish water diversion guidelines that strike a balance between off-stream uses (agriculture and hydroelectric power production) and instream uses of this water, including maintenance and restoration of stream and riparian habitat and ecosystems as well as protection of traditional and customary Hawaiian rights.
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