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TECHNICAL REPORT
VADOSE ZONE PROCESSES AND CHEMICAL TRANSPORT

Artificial Recharge of Humic Ground Water

DHI Water & Environment, Agern Allé 11, DK-2970 Hørsholm, Denmark

Corresponding author (chg{at}dhi.dk)

Received for publication June 11, 1999.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
The purpose of this study was to investigate the efficiency of soil in removing natural organic matter from humic ground waters using artificial recharge. The study site, in western Denmark, was a 10000 m² football field of which 2000 m² served as an infiltration field. The impact of the artificial recharge was studied by monitoring the water level and the quality of the underlying shallow aquifer. The humic ground water contained mainly humic acids with an organic carbon (OC) concentration of 100 to 200 mg C L^-1. A total of 5000 m³ of humic ground water were sprinkled onto the infiltration field at an average rate of 4.25 mm h^-1. This resulted in a rise in the water table of the shallow aquifer. The organic matter concentration of the water in the shallow aquifer, however, remained below 2.7 mg C L^-1. The organic matter concentration of the pore water in the unsaturated zone was measured at the end of the experiment. The organic matter concentration of the pore water decreased from 105 mg C L^-1 at 0.5 m to 20 mg C L^-1 at 2.5 m under the infiltration field indicating that the soil removed the organic matter from the humic ground water. From these results we conclude that artificial recharge is a possible method for humic ground water treatment.

Abbreviations: ADOC, acid desorbable organic carbon • CPM, counts per minute • DOM, dissolved organic matter • EC, electrical conductivity • MBS, meters below surface • NDOC, non-acid desorbable organic carbon • NPOC, non-purgeable organic carbon • OC, organic carbon • PTFE, polytetrafluoroethylene • TOC, total organic carbon

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
GROUND waters with non-purgeable organic carbon (NPOC) concentrations of less than 3 mg C L^-1 are the main source for drinking water in Denmark. Ground waters rich in natural organic matter are found in several regions of Denmark, in other European countries (Alborzfar, 1996), and the USA (Tan and Amy, 1991; Tan and Sudak, 1992). The natural organic matter in aquifers can be partially decomposed remains of the terrestrial plants or marine organisms originating from the deposition of the aquifer sediments. Alternatively, organic matter from topsoil or surface waters can be brought into the aquifer with infiltration. In ground water, dissolved organic matter (DOM) is mostly humic substances and hydrophilic acids. Humic substances can make up 50 to 80% of the DOM (Grøn et al., 1989). Ground waters with high DOM contents and a high fraction of humic substances are termed humic ground water.

The conventional drinking water treatment processes in Denmark are simple aeration and sand filtration and they have been combined with coagulation techniques to remove organic matter from humic raw water. This technique is based on the addition of a coagulant, such as Al₂(SO₄)₃, to the water. The efficiency of coagulation depends upon the raw water composition (e.g., the type of humic substances, ion concentrations, and pH). As an alternative, membrane filtration processes have been studied in humic ground water treatment (Alborzfar et al., 1994, 1998).

Artificial recharge methods aim to enhance natural recharge in order to increase the amount of available ground water. These include surface recharge (e.g., water spreading and recharging through pits and basins) (De Jonge, 1994) and well injection (Walton, 1991; Bouwer, 1994; Karimi et al., 1998). Artificial recharge has also been practiced to reduce, balance, or reverse saltwater intrusion by fresh water storage in aquifers (Piet and Zoetman, 1980). Taking advantage of physical, chemical, and biological processes occurring within the soil, artificial recharge has been successfully applied to potable water production (Sontheimer, 1980), improving ground water and lake water quality for nonpotable reuse (Villumsen et al., 1993), and waste water treatment (Bouwer, 1985; Wilson et al., 1995; Kanarek and Michail, 1996).

Surface artificial recharge of ground water requires permeable topsoils (sandy loam, sand, and gravel), an unsaturated zone without extremely low-permeability layers (e.g., clay and silt) that could cause development of perched ground water, and aquifers with sufficient lateral flowthrough to prevent excessive mounding. Vegetation, by grass or other shallow-rooted vegetation, increases deep percolation of water through the soil (Bouwer, 1994). The thickness of the unsaturated zone is an important factor to achieve a sufficient contact time between the soil and water. A thick unsaturated zone also prevents ground water interference with the infiltration process.

In this study, surface artificial recharge was studied for humic ground water treatment. This paper discusses the effectiveness of soil to remove natural organic matter from humic ground water during its infiltration through the unsaturated zone.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Experimental Site
The experimental site was a 10000 m² football field located in western Denmark. A subarea of approximately 2000 m² was used as an infiltration field. The remaining area served as the observation field.

Site Geology
The site geology consists of sands and clayey sands to a depth of approximately 10 m. This forms a shallow unconfined aquifer with a ground water table at approximately 5 meters below surface (MBS). The shallow aquifer is underlain by a 10-m-thick clay layer below which are sands and gravels to a depth of 77 m. Between 77 and 94 m is an aquifer sandwiched between two clay layers, which contains the humic ground water used for this experiment (Fig. 1) . The humic ground water well was installed to a depth of 94 MBS. The well screened in two intervals at 69.3 to 76.3 m and 79.3 to 92.3 m and produced 20 m³ of water per hour. In order to maintain a high organic matter concentration in the water, the upper-screened interval was closed in the spring.

View larger version (84K): [in this window] [in a new window]   Fig. 1. Geological cross-section of the study site. MBS, meters below surface

View larger version (18K): [in this window] [in a new window]   Fig. 2. Top view of the study site. A and B show the locations where the sieve analyses were carried out. OB1 through OB10 indicate observation wells outside the infiltration field. OBI1 through OBI4 refer to observation wells inside the infiltration field. S1 through S3 show sampling points upgradient, under the infiltration field, and downgradient, respectively. A,B,C designates the place where the cup sampled pore waters were collected during the sampling. B1, B3, B4, B5, and B6 are the locations where soil samples were taken

Gamma logging of the site was carried out along the infiltration field (in five wells: OBI1, OBI2, OBI3, OBI4, and SWD2, a 7.5-m-deep sampling well at S2) and across the site from the east to west (in four wells: OBI1, OBI2, OB3, and OB8) (Fig. 4) . The gamma log records natural radioactivity within a few tens of centimeters of the borehole wall, and in a sedimentary sequence picks out the clay and silts that have higher activity than sands and gravels (Griffiths and King, 1981). From comparison of the activity with the geological descriptions of the sediment samples in hand auger borings B3, B1, and B6, a activity greater than 700 counts per minute (CPM) was assigned to clayey deposits.

View larger version (19K): [in this window] [in a new window]   Fig. 4. Gamma logging data for the study site. Values greater than 700 counts per minute (CPM) correlate to low permeable clay and silt layers. SWD2 refers to the 7.5-m-deep well at the S2 sampling point under the infiltration field. MBS, meters below surface

Origin and Characteristics of the Dissolved Organic Matter in the Deep Ground Water
The DOM of the ground water in the deep aquifer originates from the marine sediments deposited during the Holstein interglacial period approximately 200000 yr ago (Krog, 1994). The DOM is 80% humic acids, 10% fulvic acids, and 10% hydrophilic acids (Krog, 1994) as obtained from the isolation procedure based upon precipitation of humic acids and separation of fulvic acids from hydrophilic acids by XAD-8 column chromatography (Krog and Grøn, 1995). The dominating humic acids exhibited a broad molecular weight distribution from above 100000 g mol^-1 to below 2000 g mol^-1 as observed by size exclusion high performance liquid chromatography (Grøn, 1991). The characteristics of the humic acids here are typical for old humic acids found in many Danish deep aquifers: a high carbon content (56.49%), a low oxygen to carbon elemental ratio of 0.46, a low content of carboxylic acid groups (220 cmol kg^-1 humic acids), and low contents of total humic bound amino acids (36 mmol kg^-1) and carbohydrates (1.9 g kg^-1) (Krog, 1994; Grøn et al., 1996). Still, these structural properties of the humic substances are very different from those found for DOM in more shallow, aerobic aquifers with more recent organic matter or in landfill leachates (Grøn et al., 1996; Christensen et al., 1998).

Sampling
The ground water quality was monitored at three locations: upgradient (S1), within (S2), and downgradient (S3) of the infiltration field (Fig. 2) before, during, and after the experiment. At each location, three wells were installed to depths of 3.5, 5, and 7.5 MBS. The design of the sampling wells was identical to that of the observation wells, except that they did not have any screen filters. The boring tip had a 10-cm-long perforated section immediately above the tip to let in the ground water. The perforated area was protected with a stainless steel net in order to prevent ingress of aquifer material into the holes. Above this, a polytetrafluoroethylene (PTFE) check valve stopped the water from leaving the pipe.

The wells were emptied twice before the sample was taken. A length of PTFE tubing was lowered into the well on top of the check valve and the other end was connected to a filtration unit. The ground water flowed through the tubing directly into the filtration unit by pressurizing the well with nitrogen gas following the procedure reported by Kjeldsen (1991). One portion of the sample was analyzed for pH, HCO^-₃, and electrical conductivity (EC) on site. The rest was filtered under pressure through a 0.1-µm cellulose nitrate membrane filter (Sartorius, Goettingen, Germany). The filtered sample was taken to the laboratory for further analysis.

Pore water samples were collected from the A (20–40 cm), B (40–100 cm), and C (100–115 cm) soil horizons with porous PTFE cup samplers, which were installed following the method reported by Beier and Hansen (1992) at three sites under the infiltration field. Each cup sampler had a 21-mm o.d. and a length of 90 mm, of which 50 mm was porous with an apparent pore size of 2 µm (Prenart Equipment Aps, Frederiksberg, Denmark). The cups were connected directly to glass bottles with PTFE tubing. By applying a vacuum of -40000 kg m^-1 s^-2 to the bottles, the pore water samples were collected. During sampling, the bottles were kept in a cool box buried in a soil pit to maintain a constant low temperature. This prevented any increase in microbial activity. The sampling bottles were replaced every 2 to 3 wk.

The soil samples were taken by a hand auger at three locations (B3, B1, and B6) inside, and at two locations (B4 and B5) outside the infiltration field (Fig. 2) at approximately 0.2 m intervals to a depth of 4.5 m immediately after completing the experiment. The samples were taken to the laboratory and stored at 8 to 10°C until analysis. Each soil sample was centrifuged at 3000 rpm for 20 min. The collected pore water from each centrifuged soil sample was filtered through a 0.2-µm prewashed cellulose nitrate membrane inline syringe filter suitable for filtering small sample volumes (Sartorius) and prepared for analyses. Since the cellulose nitrate 0.1-µm inline syringe filters were not available and other available 0.1-µm filter materials contaminated the filtrates with excess organic matter, 0.2-µm filters were used for filtration.

The total organic carbon (TOC) was determined in the dried soil samples. The samples were decarbonatized with nitric acid (2 M) in two or more steps. The supernatant was centrifuged off followed by determination of its NPOC, yielding acid desorbable organic carbon (ADOC). The OC of the remaining dried, solid phase was determined subsequently, yielding the non-acid desorbable organic carbon (NDOC). Total organic C was obtained as ADOC + NDOC. All results were given as percent C of dry weight of the original sample.

Analytical Methods
Solutions and dilutions were prepared in Milli-Q pure water (Millipore, Bedford, MA) and chemicals were of pro analysis quality from Merck (Whitehouse Station, NJ). A summary of the standard analytical methods used is shown in Table 1.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

The high chloride contents, the slightly alkaline pH, the high bicarbonate, the low calcium, and the high NPOC are typical of humic ground waters (Trona waters) found mainly in deep aquifers in marine sediments in Denmark, northwestern Europe, and parts of the USA.

Irrigation
The humic ground water was distributed on the infiltration field through an irrigation system consisting of six sprinklers (Fig. 2). Irrigation was carried out for 3 h per day during the fall and winter, for 6 h per day during the spring, and 9 h per day during the summer. No irrigation was carried out while the site was covered with snow during the wintertime. During the total irrigation time of 588 h, 5000 m³ of humic ground water were spread over the infiltration field (2000 m²). The monthly precipitation was recorded at a local meteorological office.

The equipotential lines of the shallow ground water table before and after the experiment are shown in Fig. 3 . The numbers here show the vertical distance from an arbitrary datum 10 m below the ground surface. The hydraulic gradient of the shallow aquifer increased 1.4 times from 0.007 to 0.010 due to infiltration. A significant rise in the ground water table was observed in particular in the eastern part of the site. This is shown by the changes in the shape of the equipotential lines in the eastern section (Fig. 3a,b). The normal ground water flow direction from the east to the west remained the same, as no significant change was observed in the center and western parts of the site.

View larger version (25K): [in this window] [in a new window]   Fig. 3. Equipotential lines for the shallow ground water table (a) before and (b) after the artificial recharge experiment. Data are in meters above an arbitrary datum

Ground Water Quality
The short sampling wells to a depth of 3.5 m in all three locations (S1, S2, and S3) were not used in sampling, as the artificial recharge did not result in such a high rise in ground water levels. Figure 5 shows the ground water composition at 5 and 7.5 m under the infiltration field during the irrigation time, and the irrigation and precipitation rates in millimeters per day. The ion concentrations and the EC of the ground water at the 5-m depth increased and approached the levels of the humic ground water (Table 2). This increase was minimal for the first two irrigation periods with a low irrigation rate, but larger during the final and longer irrigation period with a higher irrigation rate. The increase in the ion concentrations and the EC of the ground water was also observed at the depth of 7.5 m. Due to a time lag for the water to move from 5 to 7.5 m, this was observed toward the end of the experiment only. The change in the composition of the ground water seen in Fig. 5 shows that the humic ground water recharged the shallow aquifer. The concentration increase in the shallow ground water was clearly seen for chloride, for example, with a comparatively small concentration difference between the infiltrating humic ground water and the shallow ground water (up to a factor of 5). Conversely, no concentration increase could be observed for NPOC with a much larger difference in concentrations (a factor of not less than 35). The low NPOC concentrations of ground water at both depths (Fig. 5) thus clearly demonstrates that organic matter was efficiently removed from the humic ground water passing through the unsaturated zone.

View larger version (20K): [in this window] [in a new window]   Fig. 5. Ground water composition at 5 and 7.5 m under the infiltration field and irrigation and precipitation rates in millimeters per day from Day 1 to Day 239. NPOC, non-purgeable organic carbon; MBS, meters below surface; EC, electrical conductivity

Regardless of the positions of the sampling sites, the NPOC concentrations of the ground water samples were below 2.7 mg C L^-1 throughout the experiment.

Cup Sampled Pore Water
Infiltration of the humic ground water increased the average concentration of Cl^- and the EC of the pore water collected from the C horizon under the infiltration field to the level of the applied ground water (Fig. 6 and Table 2). The gap in the data in Fig. 6 was due to the absence of irrigation and sampling during the winter.

View larger version (19K): [in this window] [in a new window]   Fig. 6. Average composition of the polytetrafluoroethylene (PTFE) cup sampled pore water in the C horizon (1.00–1.15 m) under the infiltration field. NPOC, non-purgeable organic carbon; EC, electrical conductivity

Three cup samplers were placed in a 5-L container of humic ground water. Three consecutive samples were collected from each cup at the same vacuum applied in the field. The cups allowed a free passage of Na⁺ and Cl^- ions but reduced the NPOC concentration by an increasing amount up to 97% (Table 3). The decreasing NPOC concentrations were probably due to the build up of a filtering layer of organic matter that was observed on the surface of the cups.

Centrifuged Pore Water from Soil Samples
As the cup samplers were suspected to alter the composition of the pore water, pore water was instead obtained by centrifugation of soil samples. These soil samples were taken from the unsaturated zone both inside and outside the infiltration field at the end of the experiment after completion of the irrigation. Figure 7 illustrates a comparison between the pore water compositions inside and outside the infiltration field. The pore water composition inside the field represents the compositions of the pore waters collected from the soil samples taken from the three hand auger borings (B1, B3, and B6) through similar geological materials. The pore water composition outside the field shows the compositions of the pore waters collected from the soil samples taken from two hand auger borings (B3 and B4) again through similar geological materials. It should be emphasized that the composition of the pore water obtained by centrifugation might have also been disturbed particularly with respect to NPOC due to the sampling, transportation, storage, and centrifugation process itself. Still, the NPOC profiles obtained with centrifuged pore water resembled the profiles obtained from analyzing soil samples for sedimentary OC (compare Fig. 7 and 8) .

View larger version (20K): [in this window] [in a new window]   Fig. 7. Average composition of the pore waters centrifuged from the soil samples taken from three hand auger borings inside (B1, B3, and B6; left) and two outside (B4 and B5; right) the infiltration field. NPOC, non-purgeable organic carbon; MBS, meters below surface; EC, electrical conductivity

View larger version (13K): [in this window] [in a new window]   Fig. 8. A comparison between the sedimentary organic carbon (OC) of the soil samples measured as acid desorbable organic carbon (ADOC) and given as percent dry weight of the original sample. The soil samples were taken from the unsaturated zone inside (B1 and B3) and outside (B4) the infiltration field from 0.45 to 3.5 meters below surface (MBS)

At a depth of 0.5 m below the infiltration field, the NPOC concentration of the pore water was 85 to 105 mg C L^-1, whereas it was only 30 mg C L^-1 outside the field. At 2.5 m, the NPOC concentrations of the pore waters both inside and outside the field were 20 mg C L^-1. Below this depth the NPOC concentrations both inside and outside the infiltration field decreased and became equal to 6 to 7 mg C L^-1 just above the ground water table.

The gradient in NPOC concentrations from 0 to 2.5 m under the infiltration field and the convergence of the deeper parts of the profiles outside and inside the infiltration field suggest that the organic matter from the humic ground water was removed from the pore water solution by the soil.

Organic Carbon in Soil Samples
The TOC (given as percent C per dry weight of the samples) was determined for the soil samples collected inside (B3 and B1) and outside (B4) the infiltration field. The solid samples showed the same trend as the centrifuged pore water, as mentioned above (data not shown). The TOC content of the samples taken between 0.15 and 2.5 m under the infiltration field was higher (0.241–0.021%) than that of the samples taken outside the field (0.072–0.016%). Between 2.5 and 4.3 m, the TOC decreased and was the same at approximately 0.022% both inside and outside the field. The ADOC of the samples taken inside and outside the infiltration field are compared in Fig. 8. The ADOC of the samples taken inside the infiltration field was greater than of the ones taken outside the field down to a depth of 2.5 MBS. Development of brownish colored soil layers between 0.5 and 1 m below the infiltration field also indicated retention of organic matter.

Retention of DOM from the infiltrating humic ground water was evident within the top 2.5 MBS, indicating an efficient contact between infiltrating water and the sediment particles and thus a dominating matrix flow pattern. Still, macropore flow might have occurred, but the effect of macropore or preferential flow would be diminished contact between the infiltrating water and the sediment matrix. The result would be an underestimation of the retention capacity of the unsaturated zone in this study.

Overall, the NPOC, TOC, and ADOC data for pore water and soil samples suggest that part of the organic matter was removed from the pore water by retention and not by degradation in the unsaturated zone. Therefore, continuous infiltration of humic water might finally exhaust the retention capacity of the unsaturated zone, when all retention sites on the sediment surfaces have been occupied by organic matter from the infiltrating water. This could probably be counteracted to some degree by application of periodical irrigation schemes, as the organic matter degradation is expected to be more efficient during dry periods with improved access of oxygen to all parts of the sediment matrix.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Artificial recharge of humic ground water at an average hydraulic loading of 4.25 mm h^-1 resulted in a rise of the ground water table of the shallow aquifer in the eastern and northeastern parts of the field. The rising ground water table demonstrated substantial infiltration of humic ground water.

The pore water centrifuged from soil samples under the infiltration field had higher EC and Na⁺ and Cl^- concentrations than the pore waters centrifuged from the soil samples collected outside the infiltration field. This demonstrated the effect of the infiltrating humic ground water on the pore water composition through the entire unsaturated zone. The NPOC concentrations of the pore water centrifuged from the soil samples under the infiltration field were up to 71% higher than that in the pore waters centrifuged from the soil samples outside the infiltration field. A steep NPOC gradient in the unsaturated zone below the infiltration field showed that the upper layer of the soil removed the natural organic matter from the humic ground water. An increase in sedimentary OC measured as TOC and ADOC in the upper part of the unsaturated zone below the infiltration field suggested retention rather than degradation for part of the removal.

Recharge of the shallow aquifer by the humic ground water increased the Na⁺, Cl^-, and Ca²⁺ concentrations and the EC of the ground water under the infiltration field. The NPOC concentration of the ground water from the shallow aquifer was always less than 2.7 mg C L^-1 regardless of the position of the sampling point. The increase in inorganic ions in the ground water and the absence of an increase in NPOC supported our suggestion that NPOC was indeed removed from the infiltrating ground water in the unsaturated zone.

Based on our study, artificial recharge may serve as a method for treatment of humic ground waters, the organic matter can be removed from the water by natural processes occurring in the soil, and finally the capacity of the unsaturated zone could be limited as part of the organic matter removal is by retention and not by degradation.

Additionally, the PTFE cup samplers should be considered unreliable for studying the fate of OC in soil as the cups filtered the organic matter from the collected pore water samples and therefore resulted in a change in the pore water composition.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Alborzfar, M. 1996. Membrane filtration and artificial recharge of humic ground waters. Ph.D. thesis. The Technical Univ. of Denmark, Lyngby.
• Alborzfar, M., C. Grøn, and G. Jonsson. 1994. Ultrafiltration in producing drinking water from humic ground waters. Environ. Int. 20:411–417.
• Alborzfar, M., G. Jonsson, and C. Grøn. 1998. Removal of natural organic matter from two types of humic ground waters by nanofiltration. Water Res. 32:2983–2994.
• Beier, C., and K. Hansen. 1992. Evaluation of porous cup soil-water samplers under controlled field conditions: Comparison of ceramic and PTFE cups. J. Soil Sci. 43:261–271.
• Bouwer, H. 1985. Renovation of wastewater with rapid-infiltration land treatment systems. p. 249–282. In T. Asano (ed.) Artificial recharge of groundwater. Butterworth Publ., Boston, MA.
• Bouwer, H. 1994. Pre-conference course on ground water and recharge principles, Orlando, FL. 17–22 July 1994. Am. Soc. Civil Eng., Reston, VA.
• Caughey, M.E., M.J. Barcelona, R.M. Powell, R.A. Cahill, C. Grøn, D. Lawrenz, and P.L. Meschi. 1995. Interlaboratory study of a method for determining nonvolatile organic carbon in aquifer materials. Environ. Geol. 26:211–219.
• Christensen, J.B., D.L. Jensen, Z. Filip, C. Grøn, and T.H. Christensen. 1998. Characterization of the dissolved organic carbon in landfill leachate polluted groundwater. Water Res. 32:125–135.
• Clesceri, L.S., A.E. Greenberg, and R.R. Trussel. 1989. Standard methods for the examination of water and wastewater. 17th ed. Am. Public Health Assoc., Washington, DC.
• De Jonge, H.G. 1994. Artificial recharge in a dune area: Forty years of experience. Proc. 2nd Int. Symp. on Artificial Recharge, Orlando, Florida. 17–22 July 1994. Am. Soc. Civil Eng., Reston, VA.
• Griffiths, D.H., and R.F. King. 1981. Applied geophysics for geologists & engineering. 2nd ed. Pergammon Press, Oxford, UK.
• Grøn, C. 1991. Bruntvandsproblemer i Danmark (Humic ground waters in Denmark). (In Danish.) Lecture notes from the 40th course on drinking water supply. Danish Water Supply Assoc., Aarhus.
• Grøn, C., B. Dinesen, and A. Villumsen. 1989. Brunt vand: Endnu en trussel imod Danmarks fremtidige vandforsyning? (Brown water: Still a threat for Denmark's future water supply?) (In Danish.) Vandteknik 75:207–212.
• Grøn, C., L. Wassenaar, and M. Krog. 1996. Origin and structures of groundwater humic substances from three Danish aquifers. Environ. Int. 22:519–534.
• Kanarek, A., and M. Michail. 1996. Groundwater recharge with municipal effluent: Dan Region Reclamation Project, Israel. Water Sci. Technol. 34:227–233.
• Karimi, A.A., J.A. Redman, R.F. Ruiz. 1998. Ground water replenishment with reclaimed water in the city of Los Angeles. Ground Water Monit. Remediation 18:150–158.
• Kjeldsen, P. 1991. Undersøgelserne ved Vejen Losseplads: Perkolatudsivning (Investigations on the Vejen landfill: Leaching). (In Danish.) Rep. P3. Laboratoriet for Teknisk Hygiejne, Danmarks Tekniske Højskole, Denmark.
• Knudsen, J. 1987. Permeabilitets- og porøsitetsbestemmelse ved kornstørrelseanalyse (Determination of permeability and porosity by sieve analysis). (In Danish.) Vandteknik 55:191–198.
• Krog, M. 1994. Aminosyrer og monosaccharider i humus fra dybe grundvandsmagasiner i Danmark (Amino acids and carbohydrates in humic substances from deep aquifers in Denmark). (In Danish.) Masters thesis. Dep. of Geology, Univ. of Aarhus, Denmark.
• Krog, M., and C. Grøn. 1995. Isolation of haloorganic groundwater humic substances. Sci. Total Environ. 172:159–162.
• Lazarus, A.L., K.C. Hill, and J.P. Lodge. 1965. A new colorimetric micro-determination of sulfate ion in automation analytical chemistry. Tech. Symp. Mediad, New York.
• Piet, G.J., and B.C.J. Zoetman. 1980. Organic water quality changes during sand bank and dune filtration of surface waters in the Netherlands. J. Am. Water Works Assoc. 72:400–404.
• Sontheimer, H. 1980. Experience with riverbank filtration along the Rhine River. J. Am. Water Works Assoc. 72:386–390.
• Stumm, W., and J.J. Morgan. 1981. Aquatic chemistry. An introduction emphasizing chemical equilibria in natural waters. 2nd ed. John Wiley & Sons, New York.
• Tan, L., and G.L. Amy. 1991. Comparing ozonation and membrane separation for color removal and disinfection by-products control. J. Am. Water Works Assoc. 83:74–79.
• Tan, L., and R.G. Sudak. 1992. Removing color from a groundwater source. J. Am. Water Works Assoc. 84:79–87.
• Villumsen, A. 1994. Kunstig infiltration, ATV møde, Kunstig infiltration af overflade vand samt vand fra "uttte kloaker" (Artificial recharge of surface water and water from leaky sewers). (In Danish.) ATV-komiteen vedr. Grundvandsforurening, Copenhagen, Denmark.
• Villumsen, A., S. Gjerlufsen, and B.H. Jensen. 1993. Infiltration af overfladevand i Haralsted- Gyrstinge- Regnmark-området, forundersøgelser, Rapport til Københavns Vandforsyning (Artificial recharge of surface water in Haralsted, Gyrstinge, and Regnmark, preliminary investigations). (In Danish.) Rep. prepared for the Copenhagen Water Supply. Inst. For Geologi og Geoteknik, Danmarks Tekniske Højskole, Lyngby, Denmark.
• Walton, W.C. 1991. Principles of groundwater engineering. Lewis Publ., Chelsea, MI.
• Wilson, L.G., D. Quanrud, R. Arnold, G. Amy, H. Gordon, and A.D. Conroy. 1995. Field and laboratory observations on the fate of organics in sewage effluent during soil aquifer treatment. p. 529–538. In T. Asano (ed.) Artificial recharge of groundwater. Butterworth Publ., Boston, MA.

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