Technical Report No. 54
EFFECT OF STORM RUNOFF DISPOSAL AND OTHER ARTIFICIAL RECHARGE TO HAWAIIAN GHYBEN-HERZBERG AQUIFERS
Frank L. Peterson, David R. Hargis
November 1971
ABSTRACT
Artificial recharge for the purpose of replenishing the fresh ground-water body in Hawaii has been deliberately practiced in a few areas for many years, and has been recognized as incidental to other practices, principally irrigation, in many areas for several decades. The effects of these various artificial recharge practices on Hawaii Ghyben-Herzberg aquifers are briefly described in this report. In recent years, the practice of artificially recharging wastewater such as storm runoff, sewage effluent, and various industrial wastes into the subsurface has become of growing importance in Hawaii. In 1970 the Kahului Development Company began construction of a collecting basin and four deep injection wells for the disposal of storm runoff from a residential development in Kahului, Maui. This presented a unique opportunity to evaluate the suitability of the site for artificial recharge and to study the possible effects recharge of storm runoff might have on the local ground-water body, both from a water quality and a hydraulic standpoint. Studies were made to determine the following information: (i) the concentrations of selected chemical and biological parameters in storm runoff from residential areas in the town of Kahului and in the ground-water body in the area of the collecting basin and injection wells for the purpose of predicting the effects of artificial recharge of storm runoff on the water quality of the existing local ground-water body, (ii) the injection rates that can be expected for the completed injection wells by means of pumping and injection tests, and (iii) the movement of the injected water by monitoring water levels and selected chemical and biological parameters at observation wells near the injection site. The results of pumping and injection tests of one completed well and one test hole indicate that the finished injection wells should be able to inject at rates in excess of 5500 gallons per minute per well if significant clogging from sediment does not occur, and if hydraulic interference between the four wells operating simultaneously is not significant. Water analyses indicate that quality of the storm runoff from the Kahului area is generally good, with low dissolved solids and low chloride concentrations. Some fecal coliform will undoubtably be introduced into the aquifer during injection of storm runoff. However, dilution of the injected runoff by the ground water and the hostile environment presented by the saline water in the disposal zone should eliminate any bacterial hazard. The most serious potential water quality problem may be a reduction in injection efficiency owing to possible well clogging by heavy sediment loads. The general water quality effects of injecting storm runoff into the ground-water body will be to decrease the dissolved solids concentration of the ground water in the vicinity of the wells.