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Chapter 6--Discussion
The Winfield Limestone, the regional confined aquifer, outcrops east of the study area and is recharged by precipitation. ground water in the Winfield then moves downgradient to the west-northwest supplying numerous domestic water wells in Lincolnville.
Clear Creek, just east of town, is an effluent stream obtaining its base flow from the Winfield and Nolans aquifers. Water-quality hydrographs for Clear Creek (Fig. 20), provide an indication of the water quality of the Winfield and that of runoff. The large fluctuations observed in December, February, and June represent runoff from recent precipitation events which cause the chloride concentrations and specific conductance to decrease. Simultaneously, the nitrate concentrations increase due to the greater leachability of nitrate during the dormant stage (December and February samples) of vegetation and soil-organisms which tend to tie-up nitrate, and to runoff of agriculturally applied nitrogen fertilizer (June sample) (Bormann, et al., 1968). In addition, baseflow in Clear Creek during the winter months would contain a somewhat greater concentration of nitrate because of the dormancy of vegetation and organisms that otherwise thrive in the stream during the summer months and utilize nitrate, thereby resulting in lower concentrations (H. O'Connor, 1987, verbal comm.).
Chemical variations representative of the Winfield aquifer are shown by the hydrographs of well L22 (Fig. 17). The well is located upgradient from most sources of contamination found in Lincolnville, although it is within 60 ft of both a cattle pen and a septic tank. The well was recased in 1953 by Mr. Riffel who installed and cemented-in 30 ft of iron surface casing (Mrs. Kaiser, written comm., 1986). As a result, water-quality constituents remain relatively constant on both a seasonal and short-term basis (Figs. 17 and 21), despite the fact that the Herington Limestone Member is at a very shallow depth in the vicinity of the well site.
Ground-water quality in well L17 also remained relatively constant on seasonal basis probably due to the long interval of grout from 20 to 35 ft in the annular space of the well (Fig. 12). The grout was apparently effective in preventing hydraulic interconnection between shallow ground water in the Herington and the Winfield.
The Herington Limestone Member of the Nolans Limestone, which is exposed along the upper banks of Clear Creek in the study area, is hydraulically separated from the Winfield aquifer by the lower Members of the Nolans and the Odell Shale. The extensive solution permeability and relatively shallow depth throughout the study area easily allow recharge by precipitation. Thus, the Herington becomes an intermittently unconfined aquifer during extended wet periods, in particular during the spring months.
Seasonal recharge to the Herington results in the seasonal leaching of water-soluble substances from the ground surface and unsaturated zone to an intermittent water-table (Pettyjohn, 1982). Recharge to the Herington occurs, for the most part, as infiltration through soils rather than direct entry through fractures or conduits. Soil infiltration can deliver to ground water greater masses and higher concentrations of nitrate, and chloride and a greater mass of pesticides than direct recharge. Recharge occurring as direct entry, or run-in water, results in high concentrations of suspended sediment, pesticides, and bacteria (Hallberg et al., 1985).
The relatively rapid and significant water-quality fluctuations, or 'spikes' exhibited by some of the water wells in the study area represent recharge to the Herington being imposed on the Winfield aquifer either directly into the individual well or into an upgradient well or borehole. A spike represents a high-concentration slug of contaminant, which has undergone little mixing with native ground water, that is entering the well (Walker, 1973).
The seasonal spikes observed in water-quality hydrographs for wells L2 and L4 (Fig. 18), represent a slug of high nitrate concentration moving through the Winfield aquifer that originated from shallow seepage into well L27 which is located at the facilities where bulknitrogen fertilizer is stored, handled, and spilled. In addition, other types of agricultural fertilizers and chemicals are stored, handled, tank-mixed, and spilled at these facilities, possibly accounting for the high chloride concentration observed at the same time as the high nitrate concentration.
Well L27 is an old well for which very little information exists. At the surface, the well is not adequately covered and appears to have some galvanized steel casing which undoubtedly leaks and is nearly flush with ground level. Therefore, seepage into this well can certainly occur from the shallow subsurface and/or directly into the top of the well. On several occasions when two samples were collected (minutes apart) from well L27, the first sample contained considerably higher concentrations of nitrate, also indicating shallow seepage into the well. The lowest nitrate concentration measured in a sample from this well was 246 mg/L.
Well L26, the elevator office well, is located very near well L27 and the above-mentioned facilities. High nitrate concentration spikes are also observed in water-quality hydrographs for this well (Fig. 16). Because the well is completed in a pit and water had been observed standing in the bottom of the pit on several occasions, the spikes may be related to shallow soil water high in dissolved nitrate overtopping the casing and draining into the well.
Well L3, which is located between wells L26 and L27, and wells L2 and L4, did not exhibit the spikes of high nitrate concentration observed in water-quality hydrographs for these other wells. Conversely, it exhibited a spike of 'fresh' water during the May 8th sampling (Fig. 16) which resulted in a greater than 10 percent decrease in concentration of the standard inorganic constituents from the September 1984 analyses. This spike resulted from soil water that had seeped into the pit of well L3 and was flowing over the top of the casing directly into the well. Although this soil water was 'fresher' with respect to dissolved inorganic constituents, it contained sufficient amounts of organic material (probably humic material and fluvic acids), to cause discoloration and give the water a pH of 6.65 and a TOC concentration of 6.12 mg/L even after one well-bore volume (110 gallons) had been discharged from the well.
Because well L3 is completed in a pit and there is another well (abandoned and unplugged) in a pit about 170 ft north, it is believed that the potential volume of 'fresh' water that entered the Winfield aquifer from these two wells, after any of the precipitation events that occurred during the spring months, was sufficient to cause the slug of high nitrate concentration that was also in the Winfield aquifer to be 'deflected' around or considerably diluted by the bulb of 'fresh' water that was formed.
However, following the decreases in well L3 were substantial increases in constituent concentrations which seemed to be maintained throughout the year except for the occasional sporadic short-term variations. Because neither this trend of ground-water quality nor the constituent concentrations were exhibited by wells L2 and L4, it is believed that ground water in the Herington containing considerably more leached constituents was entering the well bore of well L3. In this case, the 25 feet of iron surface casing in this well was not adequate, either in length or installation, to prevent hydraulic interconnection between the Herington and the Winfield.
Well L5, located just east of the aforementioned facilities, did not exhibit spikes of high nitrate concentration in its water-quality hydrographs similar to those observed in wells L2, L4, and L26, further confirming the direction of ground-water flow in the Winfield to be to the west-northwest. However, well L5 did show a similar pattern of elevated chloride concentration early in the study as exhibited by well L3 (Fig. 16). In addition, a small peak in nitrate concentration occurred in July 1985, one month after the peak concentrations were observed in wells L2 and L4. Even though nitrate concentration data for ground water from Well L5 was not available before January 1985, it is believed that possibly movement toward and seepage into the well had been induced by pumpage of wells east of the railroad for irrigating corn grown in the east right-of-way of the railroad (Albert Riffel, verbal comm., 1985).
Construction details for well L5 suggest that this occurrence is possible, because the well was recased in 1953 using only 12 feet of iron surface casing and 75 feet of galvanized steel casing. Therefore, the Herington Limestone could be exposed to leaky and possibly corroded galvanized steel casing (Fig. 13).
The short-term 'spikes' of appreciably high or low constituent concentrations exhibited by several wells in the study area occurred on a seasonal basis during periods of increasing rainfall, and in some cases in direct response to a precipitation event. They are probably the result of contaminated or 'fresh' water slugs that have entered the Winfield aquifer from the Herington or the soil zone by way of boreholes, whether a new or old domestic or an old abandoned and unplugged well, and have moved downgradient into a well being sampled.
However, water-quality hydrographs for other wells exhibited a different seasonal trend in which constituent concentrations began increasing as early as February and March when warmer temperatures caused frozen conditions in the soil to thaw and allowed infiltration of soil moisture. In general, these increases were initially gradual but became greater with increased precipitation and usually reached a maximum in June. (This is the same trend exhibited by the water level fluctuations in the study area shown in Figure 15).
An example of such a seasonal trend in chloride and specific conductance was exhibited by well L10 (Fig. 18). The increases were also evident in hydrographs from the previous county study (O'Connor et al., in preparation) (Fig. 1) and probably represent recharge to the Herington that resulted from precipitation leaching highway deicing salts applied to Highway 56/77. An insufficient grout interval (Fig. 11) and the proximity of the well to the highway could allow recharge water to enter the Herington, and then reach the annular space of the well and drain downward to the Winfield aquifer. This pathway was supported by a substantial increase in chloride concentration exhibited on a short-term basis (Table 2) subsequent to a major rainfall event in early May 1985.
The large water quality variations, both seasonal and short-term exhibited by well L19 (Figs. 19 and 21, and Table 2) confirm the suspected inadequacy of the grout seal in the annular space of the well (Fig. 14). In this well, the Herington Limestone Member is hydraulically connected to the Winfield aquifer. The well appeared at the surface and from data in the water Well Record to meet minimum standards. However, the activities of the well owners at the ground surface in the vicinity of the well were reflected in the quality of the well water. The owners applied the following chemicals once a year to their property: Chlordane around the outside of the house, nitrogen and phosphorus fertilizers on the yard and garden in the fall, and 2-4-D to the yard to kill dandelions and other broad leaf weeds. Leaching and transport through the soil into the Herington of some of the soluble chemicals and other soil constituents in the vicinity of the well probably occurs. Once in the Herington the water moves to and drains down the well bore to the Winfield aquifer because of the inadequate grout seal (Fig. 14), and causes appreciable increases in constituent concentrations in ground water from well L19 in the spring and early summer period and high TOC concentrations.
The setting of Well L20 is almost identical to that of Well L19 except that there are two old abandoned wells at the site. One of the wells was reported to be plugged and covered. The other well (L23) was used in the study to measure water levels and was inadequately covered. The owners of the site reported applying fertilizer to their yard in the spring of 1984 and that they only do so every two or three years. The nitrate-concentration hydrograph for well L20 has both similarities to and differences from that of well L19 (Fig. 18). First, both begin at an excessive nitrate concentration (> 45 mg/L), then show a similar decline and stabilization in concentration in the fall through late winter period. Then, as the concentration increases towards another peak in May 1985 for well L19, that of well L20 decreases slightly, followed by a small increase by May 8th, then remains relatively constant through the rest of the study period.
The trends exhibited by these hydrographs may be related to the applications of nitrogen fertilizer as reported by the well owners. Fall applications could have been observed in the spring/summer at well L19, while a single application in the spring of 1984 probably caused the peak prior to the start of the study at well L20, then by late fall evidence of the application had disappeared.
The average rate of nitrogen fertilizer application to turf lawn has been estimated to range from 1.46 to 3 lbs N/1000 sq ft (Porter, 1980). Approximately 60 percent of the nitrogen from this source can eventually reach ground-water bodies (Katz et al., 1980). One study showed that inorganic nitrogen fertilizer applied in early October had virtually disappeared from the soil profile (top 20 inches) by mid-March (Porter, 1980).
Shallow intermittent ground water in the Herington could contain less total-dissolved inorganic constituents due to short residence time, but also could contain organic material and other contaminants. A greater than 10 percent decrease in the inorganic constituent concentrations between the September 1984 and the May 1985 samplings, a decrease in chloride concentration and specific conductance on a short-term basis, and the owners' reports of 'dirty' and 'lake-odor' water produced by well L20 during wet periods fit this interpretation. This could also partially explain the TOC concentration of 4.38 mg/L in well L20 on May 8th and a fecal streptococcus bacteria count of 10 per 100 mL of sample on May 20th.
The most numerous recorded occurrences of dissolved gases, sediment, discoloration, and/or odor in ground water from the sampled wells were in the spring and early summer months. However, these observations were influenced by several factors: if the sample was collected from an inside-the-house tap these occurrences would not have been as apparent; if water was allowed to discharge into a container, a better visual examination was possible; less attention to such occurrences was taken during sample collection early in the study; and problems in the pump or piping system of a well might have introduced air into the water sample.
The methane concentrations, ranging from 0.1 to 2.7 micrograms per liter (µg/L), found in the samples collected May 8th were considered to be low (Judson, verbal comm., 1985). concentrations of VOC's and the dissolved gases methane, oxygen, and carbon dioxide, were undoubtedly affected by the method of sampling, especially where variable displacement pumps were used, such as the submersible and Jet pumps in all of the wells in the study area. Barcelona et al., (1984), investigated positive displacement types of ground water sampling equipment in a laboratory setting under ideal conditions. Even though positive displacement pumps, as opposed to variable displacement types, are extensively used in ground water monitoring wells, their research showed that several types of the sampling mechanisms caused varying amounts of degassing and loss of volatiles.
The dissolved oxygen concentrations in the samples ranged from 0.5 to 6.5 mg/L (Fig. 23). The concentrations may be typical of ground water from depths comparable to those of the water wells used in the study area (75 to 115 ft in depth). The solubility of oxygen in water at 5 °C and atmospheric pressure is 12.8 mg/L and it decreases with higher temperature to 7.5 mg/L at 30 °C. The oxygen content of ground water at depths greater than 100 to 150 feet is often low, because it is consumed by the oxidation of organic matter as the water flows through both the vadose and saturated zones (Driscoll, 1986). The highest dissolved oxygen concentration observed, 6.5 mg/L, in the sample from well L19 probably represents the rapid flushing of very shallow water into the 107 ft-deep well.
The highest concentration of dissolved carbon dioxide was also found in the sample from well L19 (40 mg/L), further indicating a shallow source where considerable biochemical and hydrochemical activities occur (Freeze and Cherry, 1979). Oxidation of the higher concentration of TOC in ground water from this well could supply some of the dissolved carbon dioxide.
Kerfoot et al., (1988), showed a general correlation between ground-water inorganic carbon and organic carbon concentrations. Their findings are in agreement with several observations by others of increased ground-water inorganic carbon concentrations due to subsurface oxidation of organic material.
The concentration of bicarbonate in the May 8th sample from well L19 was comparatively higher than for all other ground-water samples (Appendix VI), indicating greater dissolution of calcium carbonate. Although the higher ionic strength of the water could account for some of the greater calcite solubility, the high concentration of carbon dioxide suggests that higher carbonic acid concentrations were more important in increasing carbonate dissolution.
Chapter 7--Conclusions
The domestic water needs of Lincolnville are supplied by private water wells tapping the Winfield Limestone aquifer. Water-well construction methods used in the area prior to 1974, when regulations governing well construction standards were established, were different from those utilized since 1974. The methods of water-well construction were found to appreciably affect the temporal variability of the ground-water quality in Lincolnville.
Water wells constructed before 1974 with a sufficient length of heavy iron surface casing extending from above ground surface down through the entire thickness of the Herington Limestone Member, produced ground water of generally good quality. concentrations of dissolved inorganic constituents were typically low and did not fluctuate significantly throughout the year.
Older wells (pre-1974) constructed without the length of iron surface casing or completed in leaky well pits allowed shallow ground water from the Herington or soil water to enter the well bore or casing, thereby hydraulically connecting these shallow zones with the Winfield aquifer. This caused water-quality variations on a seasonal and often times short-term basis.
Although the minimum standards improved water wells constructed since 1974, many of the newer wells in the study area exhibited seasonal and short-term water quality fluctuations similar to those observed in the older wells. These fluctuations were also the result of hydraulic interconnection between the Herington and the Winfield due to an inadequate grout seal in the annular space of the well. Two common problems that were identified as causing an inadequate grout seal were an insufficient annular space for effective grout placement and an insufficient length or grouted interval to seal out the entire thickness of the Herington Limestone Member. Newer wells that were constructed with an adequate grout seal, such that hydraulic interconnection between the Winfield aquifer and water in the soil or Herington was prevented, produced ground water that showed very little tempo~al variation in quality. However, such wells that were located downgradient of other wells with a hydraulic interconnection, produced ground water exhibiting short-term variations in quality on a seasonal basis.
The seasonal trend most commonly observed in the ground water from wells monitored monthly consisted of declining or stabilized constituent concentrations from late summer through late winter. In early spring through early summer concentrations increased, coincident with increasing precipitation. Short-term water-quality fluctuations were most often observed during this latter period.
The frequency and amplitude of the water quality variations were dependent upon the quantity and quality of soil water and the shallow ground water in the Herington Limestone Member and the construct10n details of the wells. Wells that allowed hydraulic interconnection between the shallow zones and the Winfield aquifer could be expected to show the greatest concentrations of nitrate, chloride, and fecal 5treptococcus bacteria. In addition, greater values of specific conductance and more dissolved gases, sediment, and sometimes discolored water were observed after periods of extended precipitation generally in the period from late winter to early summer.
Wells located near point or line sources of nitrate contamination commonly exhibited fluctuations in water quality in which nitrate concentrations often exceeded the MCL of 45 mg/L as NO3 established for public drinking water supplies. In some cases nitrate concentrations exceeded the MCL by several times. A major source of nitrate contamination was a bulk-nitrogen fertilizer storage and handling facility in the northwest part of Lincolnville. Another source of nitrate contamination believed to be responsible for elevated concentrations in some of the wells was application of nitrogen fertilizers to yard and garden areas.
The study indicates that if minimum construction standards do not preclude the possibility of hydraulic interconnection of the Winfield aquifer and water in the soil or Herington Limestone Member in domestic water wells constructed during the period from 1974 to May 1987, the quality of ground water produced could pose a threat to public health. The current regulations on minimum well-construction standards, as of May 1987, provide a greater degree of protection than the past regulations that were in effect during the period of this study, because they require a minimum of 20 ft of grout in the annular space or to a minimum of five feet into the first clay or shale layer, if present, whichever is greater. It is further required that waters from two or more separate aquifers shall be separated from each other in the borehole by sealing the borehole between the aquifers with grout.
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Kansas Geological Survey, Geohydrology
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