The effects of the Penry Wellfield on well-water quality

Ohio Journal of Science, The, Dec, 2007 by Keith O. Mann

ABSTRACT. Water samples collected during three phases (Background, Pumping and Recovery) of a year-long study in Delaware County, Ohio, document groundwater quality and the effects of pumping up to 1,500 gpm from the City of Delaware's Penry Wellfield on nearby well-water quality. Study-phase means of pH ranged from 6.84--6.99 and alkalinity means varied from 352--371 mg/L (as CaC[O.sub.3]), while specific conductance means exceeded 825[micro]S/cm, disolved solids means exceeded 499 mg/L, hardness means exceeded 525 mg/L (as CaC[O.sub.3]), and iron means exceeded 2.45 mg/L. The turbidity medians for all study phases exceeded 0.75 NTU. No significant links, either in a predictive or general sense, between water-quality parameters and well depth, flow path, time, or combinations of these variables existed. The average pH of the Background Phase (6.99) differed significantly ([alpha]=0.05) from both the Pumping Phase (6.89) and the Recovery Phase (6.84) and the mean alkalinity concentration of the Pumping Phase (352 mg/L) differed significantly from the Background Phase (371 mg/L). The Pumping Phase experienced significantly larger dissolved solids concentrations (639 mg/L) than either the Background Phase (499 mg/L) or the Recovery Phase (521 mg/L); however, no significant differences were detected with respect to specific conductance, hardness, or iron concentrations. The turbidity median of the Background Phase (0.75 NTU) differed significantly from both the Pumping Phase (1.48 NTU) and the Recovery Phase (1.36 NTU) medians and turbidity values routinely (52%) exceeded 1.0 NTU. Finally, pumping did not cause [H.sub.2]S concentrations to rise above detectable levels.

INTRODUCTION

The City of Delaware, Ohio, faces problems that a number of municipalities in Ohio and the Midwest face: providing ample, safe drinking water to a growing population. The City of Delaware used the Olentangy River as the sole source for drinking water until 1994 when the city brought into operation three wells, providing a total of 1,000 gpm, on the grounds of their water treatment plant. Soon thereafter, the city realized a need for an additional source of groundwater to blend with Olentangy River water when this surface water contains undesirable levels of agricultural contaminants, which occurs intermittently from April through September. In 1998, based on the findings of earlier studies (Ground Water Associates 1991, Ground Water Associates 1992), the city began to explore areas close to the water-treatment plant to establish an additional wellfield. During the early stages of that investigation, conducted by Collector Wells International Inc., the city purchased land on Penry Road, 5.6 km north of Delaware. After three 30.38 cm diameter production wells (TW-4, 65.5 m deep; TW-5,62.8 m deep; and TW-6a, 71.6 m deep) were drilled (Fig. 1), Collector Wells International Inc. performed several pump tests and determined the Penry Well field could supply 1,500 gpm. The study also noted that wells less than 15.2 m (50 ft.) deep within a 3.2 km (two mile) radius of the wellfield could be at a &watering risk during well field operation. In fact, during the 1998 pump tests, several wells near the wellfield experienced significant water-level declines.

Sometime after the completion of the well tests, a number of residents living near the wellfield became concerned about the potential impact of the wellfield on groundwater supply and quality and voiced their concerns to the local press and the City of Delaware. Because of these worries, the City of Delaware and its consultant, Malcolm Pirnie Inc., initiated an investigation designed to document the effects (both on groundwater quantity and quality) of the Penry Wellfield on residential wells within a 3.2 km radius of the wellfield. Collector Wells International Inc. was primarily responsible for supervising the study and collecting water-level measurements, while faculty and students at Ohio Wesleyan University concentrated on the water-quality portion of the study. Other agencies and people also contributed to this study, including the Ohio Department of Natural Resources, the Delaware Department of Health, and many residents of Troy Township. This report focuses on the water quality within a 3.2 km radius of the Penry Wellfield and so presents only a portion of the data collected and included in the comprehensive report of Collector Wells International Inc. (2001). Whereas earlier studies (Ground Water Associates 1991, Ground Water Associates 1992, Collector Wells International Inc. 1998), concentrated on locating and establishing a wellfield that could provide sufficient quantities of safe groundwater to fulfill the needs of the city, this present report, building on that earlier work, addresses solely the potential impact on water quality caused by the wellfield.

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Geologic and Hydrologic Setting

Physiographically, Delaware County lies within the Till Plains of the Central Lowlands, immediately west of the Allegheny Plateau. The topography of Delaware County, led Westgate (1926) to remark "... the most striking scenic feature of the county is its flatness." Regionally, the study area lies upon the eastern flank of the Findlay Arch with Paleozoic bedrock units dipping gently (~4 m/km) eastward, toward the Appalachian Basin (Fig. 1), with tills of the Scioto Lobe, deposited during the Wisconsinan, covering the Paleozoic bedrock. The northern border of the Broadway Moraine lies immediately south of Penry Road and the St. Johns Moraine rests 21 km to the north, outside the study area.