Protection of Food Crops During Rapid Development of the Palinpinon Geothermal Project

Abstract

A tropical water plant known as kangkong is cultivated in the Okoy River. Many hundred of people are involved in growing this important green vegetable which is harvested up to 12 times per year, hence the need to avert major damage to crops is clear. Trials suggest that kangkong is sensitive to lower levels of arsenic than boron, but because of the relative amounts of these elements in geothermal waters boron is likely to be the limiting element in regard to surface waste water discharges. Arsenic or boron toxicity symptoms were more severe in the presence of sulphate, while high calcium levels delayed the onset or reduced the severity of symptoms. Plants tolerated thermal shocks up to about 50°C for 30 minutes. Under the test conditions the maximum continuously tolerable level of geothermal fluid was about 8% and of As and B about 3 mg/kg and 5 mg/kg respectively. For purposes of crop protection during project development, however, wastewater discharges from wells under tests are normally regulated so that the level of B upstream of the cropping area does not normally exceed about 3 mg/kg.