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In recent years, Baltimore's filtration plants have experienced difficulties in their operations as a result of algal blooms in the city's impoundment reservoirs. Correctional treatment in the plants has been costly, and problems of this nature are expected to increase in the future. Such algal blooms are the result of increased levels of nutrient wastes in surface waters. The author points out that federal, state, and local agencies must all work together to limit the discharging of nutrient wastes into watersheds, thereby reducing the risk of contamination to surface waters. It is true that the quality of surface waters may be adversely affected by the group of microscopic aquatic organisms identified as algae.1 These organisms take on particular importance when surface waters are utilized as a source for community water supplies. Algae may cause undesirable changes in the physical-chemical characteristics of waterchanges in color, pH, alkalinity, carbon dioxide levels, dissolved oxygen levels, and potability. Difficulties in the treatment of these waters may result, and adjusting treatment methods may involve considerable expense. Algae of significance in water supplies have been characterized by Palmer2 into four basic groups: diatoms, the greens (Chlorophyta), the blue-greens (Cyanophyta), and the pigmented flagellates. Planktonic or free-floating algae are generally much more significant than attached or benthic forms when large and relatively deep reservoirs are used as a source of water supply. Some species will clog filters in treatment plants thereby reducing filter runs.1 Certain species of green algae, when present in sufficient amounts, may cause the pH of water to increase from 1 to 3 units.3 Several species of blue-green algae have been associated with taste-and-odor problems in water.3 The surface-water reservoirs utilized by the City of Baltimore as sources of water supply experience problems related to the seasonal occurrences of problem-causing algae. Difficulties associated with these organisms have occurred in the headwaters and the main bodies of two reservoirs and in treatment facilities. These water-quality problems have worsened dramatically in recent years. The Baltimore surface-water system serves approximately 1.5 million consumers in the metropolitan Baltimore area. Surface-water supplies originate in the Gunpowder River and north branch of the Patapsco River watersheds, which are in the central Maryland Piedmont plateau. The two watersheds encompass a total of 467 sq mi. Only 6 per cent of this land is owned by the city. However, exclusive rights to all the water contained therein have been granted to the city by the state legislature. The Gunpowder watershed encompasses the bulk of northern Baltimore County and the northeast portion of Carroll County and extends into Pennsylvania. It contains the upstream Prettyboy reservoir and the downstream Loch Raven reservoir, which have respective storage capacities of 20 and 23 bil gal. From the Loch Raven reservoir, water is furnished to the Montebello filtration plants in the northeastern part of the city. These facilities, in service for over half a century, were designed to treat high-quality surface water and employ conventional water-treatment processes that include prechlorination, alum flocculation-coagulation, sedimentation, and rapid sand filtration. |
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