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USGS1999

Cobalt-rich ferromanganese crusts in the Pacific

Co-rich Fe-Mn crusts occur throughout the Pacific on seamounts, ridges, and plateaus where currents have kept the rocks swept clean of sediments at least intermittently for millions of years. Crusts precipitate out of cold ambient sea water onto hard-rock substrates forming pavements up to 250 mm thick. Crusts are important as a potential resource for Co, Ni, Pt, Mn, Tl, Te, and other metals, as well as for the paleoclimate signals stored in their stratigraphic layers. Crusts form at water depths of about 400 to 4000 m, with the thickest and most Co-rich crusts occurring at depths of about 800 to 2500 m, which may vary on a regional scale. Gravity processes, sediment cover, submerged and emergent reefs, and currents control the distribution and thickness of crusts on seamounts. Crusts occur on a variety of substrate rocks that generally decrease in the order, breccia, basalt, phosphorite, limestone, hyaloclastite, and mudstone. Because of this wide variety of substrate types, crusts are difficult to distinguish from the substrate using remotely sensed data, such as geophysical measurements, but are generally weaker and lighter-weight than the substrate. Crusts can be distinguished from the substrates, however, by their much higher gamma radiation levels. The mean dry bulk density of crusts is 1.3 g/cm3, the mean porosity is 60%, and the mean surface area is extremely high, 300 m2/g. Crusts generally grow at rates of 1 to 10 mm/Ma. Crust surfaces are botryoidal, which may be modified to a variety of forms by current erosion. In cross-section, crusts are generally layered, with individual layers displaying massive, botryoidal, laminated, columnar, or mottled textures. Characteristic layering is persistent regionally in the Pacific. Crusts are composed of ferruginous vernadite (δ-MnO2) and X-ray amorphous Fe oxyhydroxide, with moderate amounts of carbonate fluorapatite (CFA) in thick crusts and minor amounts of quartz and feldspar in most crusts. Elements most commonly associated with the vernadite phase include Mn, Co, Ni, Cd, and Mo, whereas those most commonly associated with Fe oxyhydroxide are Fe and As. Detrital phases are represented by Si, Al, K, Ti, Cr, Mg, Fe, and Na; the CFA phase by Ca, P, Sr, Y, and CO2; and a residual biogenic phase by Ba, Sr, Ce, Cu, V, Ca, and Mg. Crusts contain Co contents up to about 2.3%, Ni to 1%, and Pt to 3 ppm, with mean Fe/Mn ratios of 0.6 to 1.3. Fe/Mn decreases, whereas Co, Ni, Ti, and Pt increase in central Pacific crusts and Fe/Mn, Si, and Al increase in continental margin crusts and in crusts with proximity to west Pacific volcanic arcs. Vernadite and CFA-related elements decrease, whereas Fe, Cu, and detrital-related elements increase with increasing water depth of crust occurrence. Cobalt, Ce, Tl, and maybe also Ti, Pb, and Pt are strongly concentrated in crusts over other metals because of oxidation reactions. Total rare earth elements (REEs) commonly vary between 0.1% and 0.3% and are derived from sea water along with other hydrogenetic elements, Co, Mn, Ni, etc. Platinum, Rh, Ir, and some Ru in crusts are also derived from sea water, whereas Pd and the remainder of the Ru derive from detrital minerals. The older parts of thick crusts were phosphatized during at least two global phosphogenic events during the Tertiary, which mobilized and redistributed elements in those parts of the crusts. 240Silicon, Fe, Al, Th, Ti, Co, Mn, Pb, and U are commonly depleted, whereas Ni, Cu, Zn, Y, REEs, Sr, and Pt are commonly enriched in phosphatized layers compared to younger nonphosphatized layers. The dominant controls on the concentration of elements in crusts include the concentration of metals in sea water and their ratios, colloid surface charge, types of complexing agents, surface area, and growth rates. Crusts act as closed systems with regard to the isotopic ratios of Be, Nd, Pb, Hf, Os, and U-series, which in part have been used to date crusts and in part used as isotopic tracers of paleoceanographic and paleoclimatic conditions. Those tracers are especially useful in delineating temporal changes in deep-ocean circulation. Research and development on the technology of mining crusts are only in their infancy. Detailed maps of crust deposits and a better understanding of small-scale seamount topography are required to design the most appropriate mining equipment.

Book chapter↗
USGS2002

Borehole-geophysical investigation of the University of Connecticut landfill, Storrs, Connecticut

A borehole-geophysical investigation was conducted to help characterize the hydrogeology of the fractured-rock aquifer and the distribution of unconsolidated glacial deposits near the former landfill and chemical waste-disposal pits at the University of Connecticut in Storrs, Connecticut. Eight bedrock boreholes near the landfill and three abandoned domestic wells located nearby were logged using conventional and advanced borehole-geophysical methods from June to October 1999. The conventional geophysical-logging methods included caliper, gamma, fluid temperature, fluid resistivity, and electromagnetic induction. The advanced methods included deviation, optical and acoustic imaging of the borehole wall, heat-pulse flowmeter, and directional radar reflection. Twenty-one shallow piezometers (less than 50-feet deep) were logged with gamma and electromagnetic induction tools to delineate unconsolidated glacial deposits. Five additional shallow bedrock wells were logged with conventional video camera, caliper, electromagnetic induction, and fluid resistivity and temperature tools. The rock type, foliation, and fracturing of the site were characterized from high-resolution optical-televiewer (OTV) images of rocks penetrated by the boreholes. The rocks are interpreted as fine- to medium-grained quartz-feldsparbiotite-garnet gneiss and schist with local intrusions of quartz diorite and pegmatite and minor concentrations of sulfide mineralization similar to rocks described as the Bigelow Brook Formation on regional geologic maps. Layers containing high concentrations of sulfide minerals appear as high electrical conductivity zones on electromagneticinduction and borehole-radar logs. Foliation in the rocks generally strikes to the northeast-southwest and dips to the west, consistent with local outcrop observations. The orientation of foliation and small-scale gneissic layering in the rocks, however, varies locally and with depth in some of the boreholes. In two of the boreholes, the foliation strikes predominantly to the northwest and dips to the northeast. Although small-scale faults and lithologic discontinuities were observed in the OTV data, no large-scale faults were observed that appear on regional geologic maps. Fractures were located and characterized through the use of conventional geophysical, OTV, acoustic-televiewer (ATV), and borehole-radar logs. The orientation of fractures varies considerably across the site; some fractures are parallel to the foliation, whereas others cross-cut the foliation. Many of the transmissive fractures in the bedrock boreholes strike about N170°E and N320°E with dips of less than 45°. Other transmissive fractures strike about N60°E with dips of more than 60°. Most of the transmissive fractures in the domestic wells strike about N60°E and N22°E with dips of more than 45°. The strike of N60°E is parallel to the trend of a thrust fault that appears on regional geologic maps. Vertical flow in the boreholes was measured with the heat-pulse flowmeter under ambient and (or) pumping conditions. Results of ATV, OTV, and conventional logs were used to locate specific zones for flowmeter testing. Ambient downflow was measured in three boreholes, ambient upflow was measured in two other boreholes, and both ambient downflow and upflow were measured in a sixth borehole. The other five bedrock boreholes and domestic wells did not have measurable vertical flow. The highest rate of ambient flow was measured in the background borehole in which upflow and downflow converged and exited the borehole at a fracture zone near a depth of 62 feet. Ambient flow of about 340 gallons per day was measured. In the other five wells, ambient flow of about 20 to 35 gallons per day was measured. Under low-rate pumping (0.25 to 1 gallon per minute), one to six inflow zones were identified in each well. Usually the fractures that are active under ambient conditions contribute to the well under pumping conditions. To prevent ambient vertical flow and the potential for cross-contamination, temporary borehole liners were installed in five of the boreholes. Specific-capacity and open-hole transmissivity values were determined in eight boreholes completed in bedrock. The specific capacity estimated for these boreholes ranges from 0.14 to 1.6 gallons per minute per foot. The values for open-hole transmissivity range over two orders of magnitude and when proportioned to individual fracture transmissivity, range from 23 to 340 feet squared per day. Two boreholes had been drilled to intersect electrically conductive zones identified by previous surface-geophysical investigations. The borehole-geophysical results indicate that the boreholes penetrate electrically conductive structures consistent with the anomalies interpreted from the surface-geophysical data. Borehole MW121R was located to intersect a dipping electrically conductive anomaly at about 60 feet, interpreted from the two-dimensional direct currentresistivity survey conducted on the western side of the landfill. The electromagnetic-conductivity log in the borehole contains a high electrical conductivity anomaly at a depth of 69 feet. The magnitude of this anomaly is nearly 10,000 millisiemens per meter and is coincident with a layer containing sulfide mineralization, rather than fractures. The other borehole, MW105R, was located to intersect another anomaly south of the landfill. This anomaly was interpreted as a north-south striking, westward dipping feature. In the borehole, two south-striking, westward dipping fractures were identified in the ATV, OTV, and radar logs. The specific conductance of the fluid measured near these fractures was as high as 1,250 microsiemens per centimeter. Water-quality samples collected in October 1999 from an isolated zone from 71.5 to 76.5 feet indicated high specific conductance (810 microsiemens per centimeter), high concentrations of iron and cadmium, negative oxidation-reduction potential, and chlorobenzene. Collectively, these parameters indicate that the high specific conductance in the borehole logs for MW105R was caused by landfill leachate. Therefore, the anomaly identified by boreholeand surface-geophysical surveys is interpreted as a conductive lithologic feature and a permeable fracture zone that contains landfill leachate.

Connecticut↗
USGS2005

Borehole-geophysical and hydraulic investigation of the fractured-rock aquifer near the University of Connecticut Landfill, Storrs, Connecticut, 2000 to 2001

An integrated borehole-geophysical and hydraulic investigation was conducted at the former landfill area near the University of Connecticut in Storrs, Connecticut, where solvents and landfill leachate have contaminated a fractured-bedrock aquifer. Borehole-geophysical techniques and hydraulic methods were used to characterize the site bedrock lithology and structure, fractures, and hydraulic properties. The geophysical and hydraulic methods included conventional logs, borehole imaging, borehole radar, flowmeter under ambient- and stressed hydraulic conditions, and discrete-zone hydraulic testing, sampling, and monitoring. The conventional geophysical-logging methods included caliper, deviation, electromagnetic induction, gamma, specific conductance, and fluid temperature. The advanced methods included optical and acoustic imaging of the borehole wall, heat-pulse flowmeter, and directional radar reflection. Borehole-geophysical methods were used to further define conductive features identified with surface-geophysical methods in the first phase of the investigation. The results of the surface- and borehole-geophysical logging were evaluated in an iterative and integrated manner to develop a conceptual model of ground-water flow at the site. The rock type, foliation, and fractures at the site were characterized from high-resolution optical televiewer (OTV) images of rocks penetrated by the boreholes and were compared to drilling logs and conventional geophysical logs. The rocks are interpreted as fine- to mediumgrained quartz-feldspar-biotite-garnet gneiss and schist with local intrusions of quartz diorite and pegmatite and minor concentrations of sulfide mineralization similar to rocks described as the Bigelow Brook Formation on regional geologic maps. Layers containing high concentrations of sulfide minerals appear as high electrical conductivity zones on electromagnetic-induction and borehole-radar logs. Foliation in the rocks generally strikes to the southwest and northeast, and dips to the northwest and southeast consistent with previous investigations in this area. The orientation of foliation, however, varies locally and with depth in some of the boreholes. These results are consistent with geologic mapping that has identified small-scale folding. The orientations of the transmissive fractures identified in the six boreholes logged for this investigation are similar to the fracture orientations mapped in a previous investigation. Many of these fractures are oriented with a north-northwest strike and have a shallow dip to the west. Other transmissive fractures have a southwest strike and dip at shallow angles to the northwest, and some strike roughly east-west and dip to the north and south. Flowmeter logging was used to identify transmissive fractures and to estimate the hydraulic properties in the boreholes. Ambient down flow was measured in one borehole, and ambient up flow and down flow were measured in another borehole. The other four bedrock boreholes did not have measurable vertical flow. Under low-rate pumping conditions (0.25 to 0.5 gallons per minute), one to three inflow zones were identified in each well. Commonly, fractures that are active under ambient conditions contribute to the well under pumping conditions. The ambient conditions were incorporated into the determination of the relative proportions of transmissivity. Specific capacity and transmissivity were determined for these open-hole low-rate pumping tests. Quasi-steady-state water levels were reached in four of the boreholes, including MW201R, MW204R, MW302R, and W202-NE. When pumped at low-rate conditions for 0.5 to 4 hours, the specific capacity ranged from 0.03 to 0.18 gallons per minute per foot. The open-hole transmissivity estimates ranged from 4.9 to 30 feet squared per day (ft2/d). Open-hole transmissivity was determined for boreholes that did not reach quasi-steady-state conditions under low-rate pumping conditions. Transmissivity was estimated for MW201R, MW202R, and MW203R using non-equilibrium methods, pumping rate, and the transient drawdown data to estimate the open-hole transmissivity. Transmissivity in these boreholes ranged from 0.98 to 3.2 ft 2 /d. The transmissivity and head of individual fractures or zones of fractures were estimated from heat-pulse flowmeter data acquired under ambient and stressed conditions. In the absence of ambient flow, data from two profiles of heat-pulse flowmeter data under two different stressed conditions were used to estimate the transmissivity and head of individual fracture zones. Only two boreholes, MW302R and W202-NE, had sufficient data for these analyses. The estimated transmissivity of individual transmissive zones ranged from 1.2 to 9.2 ft 2 /d. The transmissivity values determined by this numerical simulation method were less than the open-hole estimations, which were 15 and 30 ft 2 /d. Transmissivity also was measured directly over discrete intervals of the borehole using a straddle-packer apparatus and constant-rate pumping tests. Pumping rates were less than or equal to 0.25 gallons per minute. These discretezone single-hole pumping tests were conducted over a short period of time, usually about 30 minutes to 1 hour in duration. Pumping continued until the test zone reached a steady-state water level or until it was determined that the zone could not yield water at the pumped rate. The estimated transmissivity of individual transmissive zones ranged from about 0.21 to 11 ft 2 /d. The zone at a depth of 197 feet in W202-NE was the only zone that had discrete-interval testing with a straddle packer and sufficient heat-pulse flowmeter data for modeling the flow and estimating transmissivity and head. The two methods produced similar results. The straddle-packer method estimated a transmissivity of 4.7 ft 2 /d, and the heat-pulse flowmeter modeling results estimated a transmissivity of 6.9 ft 2 /d. A comparison of the transmissivity estimates indicate estimates typically are within an order of magnitude. The heat-pulse flowmeter methods used in this investigation to determine transmissivity of the boreholes and the individual fractures measure only the upper two or three orders of magnitude of transmissivity. Hence, other fractures in these boreholes permit the movement of water; their transmissivities, however, are lower than the detection limits of the methods that were used for this investigation and very small compared to the transmissive fractures that were studied. The data collected in this investigation were used to design discrete-zone monitoring systems for four of the boreholes used for monitoring. The results of the investigation are useful for refining the conceptual site model of ground-water flow, and for providing critical information for interpreting the results of water-quality sampling.

Connecticut↗
USGS2016

Groundwater and surface-water interaction, water quality, and processes affecting loads of dissolved solids, selenium, and uranium in Fountain Creek, near Pueblo, Colorado, 2012–2014

In 2012, the U.S. Geological Survey, in cooperation with the Arkansas River Basin Regional Resource Planning Group, initiated a study of groundwater and surface-water interaction, water quality, and loading of dissolved solids, selenium, and uranium to Fountain Creek near Pueblo, Colorado, to improve understanding of sources and processes affecting loading of these constituents to streams in the Arkansas River Basin. Fourteen monitoring wells were installed in a series of three transects across Fountain Creek near Pueblo, and temporary streamgages were established at each transect to facilitate data collection for the study. Groundwater and surface-water interaction was characterized by using hydrogeologic mapping, groundwater and stream-surface levels, groundwater and stream temperatures, vertical hydraulic-head gradients and ratios of oxygen and hydrogen isotopes in the hyporheic zone, and streamflow mass-balance measurements. Water quality was characterized by collecting periodic samples from groundwater, surface water, and the hyporheic zone for analysis of dissolved solids, selenium, uranium, and other selected constituents and by evaluating the oxidation-reduction condition for each groundwater sample under different hydrologic conditions throughout the study period. Groundwater loads to Fountain Creek and in-stream loads were computed for the study area, and processes affecting loads of dissolved solids, selenium, and uranium were evaluated on the basis of geology, geochemical conditions, land and water use, and evapoconcentration. During the study period, the groundwater-flow system generally contributed flow to Fountain Creek and its hyporheic zone (as a single system) except for the reach between the north and middle transects. However, the direction of flow between the stream, the hyporheic zone, and the near-stream aquifer was variable in response to streamflow and stage. During periods of low streamflow, Fountain Creek generally gained flow from groundwater. However, during periods of high streamflow, the hydraulic gradient between groundwater and the stream temporarily reversed, causing the stream to lose flow to groundwater. Concentrations of dissolved solids, selenium, and uranium in groundwater generally had greater spatial variability than surface water or hyporheic-zone samples, and constituent concentrations in groundwater generally were greater than in surface water. Constituent concentrations in the hyporheic zone typically were similar to or intermediate between concentrations in groundwater and surface water. Concentrations of dissolved solids, selenium, uranium, and other constituents in groundwater samples collected from wells located on the east side of the north monitoring well transect were substantially greater than for other groundwater, surface-water, and hyporheic-zone samples. With one exception, groundwater samples collected from wells on the east side of the north transect exhibited oxic to mixed (oxic-anoxic) conditions, whereas most other groundwater samples exhibited anoxic to suboxic conditions. Concentrations of dissolved solids, selenium, and uranium in surface water generally increased in a downstream direction along Fountain Creek from the north transect to the south transect and exhibited an inverse relation to streamflow with highest concentration occurring during periods of low streamflow and lowest concentrations occurring during periods of high streamflow. Groundwater loads of dissolved solids, selenium, and uranium to Fountain Creek were small because of the small amount of groundwater flowing to the stream under typical low-streamflow conditions. In-stream loads of dissolved solids, selenium, and uranium in Fountain Creek varied by date, primarily in relation to streamflow at each transect and were much larger than computed constituent loads from groundwater. In-stream loads generally decreased with decreases in streamflow and increased as streamflow increased. In-stream loads of dissolved solids and selenium increased between the north and middle transects but generally decreased between the middle and south transects. By contrast, uranium loads generally decreased between the north and middle transects but increased between the middle and south transects. In-stream load differences between transects appear primarily to be related to differences in streamflow. However, because groundwater typically flows to Fountain Creek under low-flow conditions, and groundwater has greater concentrations of dissolved solids, selenium, and uranium than surface water in Fountain Creek, increases in loads between transects likely are affected by inflow of groundwater to the stream, which can account for a substantial proportion of the in-stream load difference between transects. When loads decreased between transects, the primary cause likely was decreased streamflow as a result of losses to groundwater and flow through the hyporheic zone. However, localized groundwater inflow likely attenuated the magnitude by which the in-stream loads decreased. The combination of localized soluble geologic sources and oxic conditions likely is the primary reason for the occurrence of high concentrations of dissolved solids, selenium, and uranium in groundwater on the east side of the north monitoring well transect. To evaluate conditions potentially responsible for differences in water quality and redox conditions, physical characteristics such as depth to water, saturated thickness, screen depth below the water table, screen height above bedrock, and aquifer hydraulic conductivity were compared by using Wilcoxon rank-sum tests. Results indicated no significant difference between depth to water, screen height above bedrock, and hydraulic conductivity for groundwater samples collected from wells on the east side of the north transect and groundwater samples from all other wells. However, saturated thickness and screen depth below the water table both were significantly smaller for groundwater samples collected from wells on the east side of the north transect than for groundwater samples from other wells, indicating that these characteristics might be related to the elevated constituent concentrations found at that location. Similarly, saturated thickness and screen depth below the water table were significantly smaller for groundwater samples under oxic or mixed (oxic-anoxic) conditions than for those under anoxic to suboxic conditions. The greater constituent concentrations at wells on the east side of the north transect also could, in part, be related to groundwater discharge from an unnamed alluvial drainage located directly upgradient from that location. Although the quantity and quality of water discharging from the drainage is not known, the drainage appears to collect water from a residential area located upgradient to the east of the wells, and groundwater could become concentrated in nitrate and other dissolved constituents before flowing through the drainage. High levels of nitrate, whether from anthropogenic or natural geologic sources, could promote more soluble forms of selenium and other constituents by affecting the redox condition of groundwater. Whether oxic conditions at wells on the east side of the north transect are the result of physical characteristics or of groundwater inflow from the alluvial drainage, the oxic conditions appear to cause increased dissolution of minerals from the shallow shale bedrock at that location. Because ratios of hydrogen and oxygen isotopes indicate evaporation likely has not had a substantial effect on groundwater, constituent concentrations at that location likely are not the result of evapoconcentration.

Colorado↗
USGS1967

Swatara Creek basin of southeastern Pennsylvania: An evaluation of its hydrologic system

Local concentrations of population in the Swatara Creek basin of Pennsylvania find it necessary to store, transport, and treat water because local supplies are either deficient or have been contaminated by disposal of wastes in upstream areas. Water in the basin is available for the deficient areas and for dilution of the coal-mine drainage in the northern parts and the sewage wastes in the southern parts. Swatara Creek drains 576 square miles just east of Harrisburg, Pa., and is the largest tributary to the Susquehanna River from the north side below Harrisburg. It rises in the southern Pocono Mountains and flows southwestward across the Lebanon Plateau. On an average day Swatara Creek discharges more than 630 million gallons into the Susquehanna River at Middletown, Pa. In a year this amounts to about 23 inches of water over the entire basin and is the residual from an average annual precipitation of 45.5 inches. During an average year the flow in Swatara Creek from the upper third of the basin above Harper Tavern is always greater than 1,300 mgd (million gallons per day) for at least 15 days and is always greater than 25 mgd for at least 350 days. The daily streamflow from the basin averages 1.1 mgd per sq mi, but yields from different areas range from 0.97 to 1.22 mgd per sq mi. These variations are caused chiefly by differences in precipitation and land cover. The area of lowest yield is in the valleys west of Tremont, and the highest yields are in the Upper and Lower Little Swatara Creek subbasins. At high and medium stages the chemical character of the water in the streams is suitable for public and private supplies. At lower stages, defending on the areas and the amounts of contamination by coal-mine drainage and sewage pollution, the natural flow may require some treatment. At low stages the chemical characteristics of the natural flow not affected by man is almost identical with that of the ground water in the area drained by the stream. In general, the total dissolved solids range from about 25 to 400 parts per million and the hardness is as much as about 300 parts per million. The ground-water increment to the base flow of Swatara Creek averages about 240 mgd, or about 8.8 inches annually, for the basin. Generally, ground-water supplies in amounts of less than 0.5 mgd can be developed south of Blue Mountain. Supplies of several million gallons per day have been developed for industrial use from the permeable limestones in the south-central part of the basin. More intensive investigation in other parts of the basin would indicate areas where supplies of more than 0.5 mgd could be developed from properly spaced wells. The chemical character of water from wells depends largely on the host rock. In highly soluble rocks water contains large amount of dissolved solids; in more resistant rocks concentrations are lower. The chemical character of unpolluted ground water generally reflects the composition of the more readily soluble minerals in the local geologic environment. Areas contaminated by septic- tank effluent may have above normal amounts of nitrate and detergent products. Except where polluted, most ground water is suitable for public and industrial uses without extensive treatment. Sites for storage of surface water exist in the part of the basin lying in the valley and ridge area. As much as 30 to 40 percent of the annual flow could be impounded for release as low-flow augmentation for dilution of mine drainage and other wastes in the basin. Low sediment yields of supplying drainage areas would ensure a long life expectancy of reservoirs at these sites. Overbank flooding of the main stem of the Swatara Creek and its tributaries has occurred many times in the past. However, it has not been a hazard because urban development has not encroached on the flood plain. An inundation map of the August 1933 flood provides a basis that urban planners may use to avoid future damage. As water in the Swatara Creek moves downstream to the Susquehanna River, the flow is influenced consecutively by a large annual rainfall on the northern valley and ridge area, the wastes of surface and subsurface coal-mining activities, and less annual rainfall on the part of the basin lying in the Lebanon Plateau area; the flow is supplemented and further influenced by many tributaries and by the industrial and domestic wastes that are carried by these secondary streams. The annual precipitation ranges from 52 inches at the east edge and 49 inches at the west edge of the mountainous part of the basin to about 41 inches at the southwestern part at Middletown. The rainfall generally is adequate during the growing season to mature the crops. The mean annual temperature at Lebanon is about 52°F, and the growing season is about 180 days. In this report the basin has been divided into eight hydrologic zones, leased on runoff, natural use of water, and chemical character of water. Four zones lie in the valley and ridge area, three lie in the Lebanon Plateau area, and one lies in the highland along the southeastern basin boundary. In each of the zones the hydrologic characteristics are virtually the same, but they may be completely different from those in adjacent zones. The boundaries of the zones generally coincide with boundaries between geologic formations, and the areas in each zone include rocks of similar influence on water. Streams in zone 4 at the northeast edge of the plateau have the highest average surface runoff from 1.2 to 1.1 mgd per sq mi whereas those in zone 2 at the northwest edge of the valley and ridge area have the lowest, about 1.0 mgd. Streams in zone 8, along the southeast edge of the basin, have the largest sustained low-flow yield, about 0.26 to 0.19 mgd per sq mi; those in zone 5 overlying the Martinsburg Shale east of Harrisburg have the smallest sustained low-flow yields, 0.03 to 0.01 mgd. Streams in the limestone area of zone 7 have the greatest range in low-flow yields in any one zone from 0.60 to 0 mgd per sq mi. Low-flow yields in zones 1 through 4 range from 0.13 to 0.03 mgd per sq mi. Surface flows from zones 1 and 2 are generally acidic and contain high concentrations of sulfate, iron, and total dissolved solids especially where contaminated with mine wastes. Surface flows from zones 3 and 4 are dilute, slightly alkaline, and suitable for public water supplies. Surface flows from zones 5, 6, and 7 are alkaline and contain moderate concentrations of dissolved solids with waters of highest hardness occurring in zone 7. Surface flows from zone 8 are dilute to moderately mineralized and are relatively high in silica concentration. Nitrate concentrations are high in surf Fee flows below sewage outfalls and in ground water contaminated by septic tank effluent and industrial wastes. Average annual sediment yields of 550 to 650 tons per square mile are characteristic of zones 1 and 2 where strip mining has destroyed the forest cover and coal culm is carried into the streams. From agricultural lands on the Martinsburg Shale in zones 5 and 6, annual sediment yields range from 300 to 350 tons per square mile; but from agricultural lands on the siliceous rocks in zone 8 and zones 3 and 4 in the valley and ridge area, the sediment yield ranges from 200 to 250 tons annually per square mile. Lowest annual sediment yields in the basin are in the forested areas of siliceous rocks in zones 2, 3, 4, and 5, and in the sinkhole topography of the limestones in zone 7 where the yield ranges from 30 to 35 tons and 50 to 60 tons per square mile, respectively. The amount of ground water that can be developed in the basin is dependent on the ability of the underlying rocks to yield water to wells. More than 300 gpm (gallons per minute) can be obtained from wells in alluvial materials in the valley bottoms and in some of the limestones where large solution channels and fractures are penetrated by the wells. From 50 to 300 gpm can be obtained from wells in loosely cemented sandstones and in fractured limestones. From 10 to 50 gpm can be developed from wells in the shales and harder sandstones. The most dense rocks will yield from 1 to 10 gpm from fractures and crevices. Most wells yield water from the upper 350 feet of the formation, for this part contains the most fractures or solution channels. Studies show that the velocity at which a contaminant will move downstream in the basin is related to the discharge of the stream at the time. At a stream discharge of about 400 mgd at Pine Grove, a contaminant in Swatara Creek would require about 40 hours to move from Pine Grove to Middletown. As a result of dispersion and dilution, the maximum concentration of the contaminant at Middletown would be less than 20 percent the concentration at Pine Grove under these conditions. An evaluation of the availability of water in the basin indicates that about I,239 mgd enters as precipitation, 630 mgd leaves as streamflow, 580 mgd is evaporated and transpired, and 56 mgd is diverted for use by man. Not all the diversions for man's use are lost to the basin, as about 27 mgd is returned as sewage for reuse. About one-fourth of the waste water is returned to the ground and the remainder to stream drainageways. Of that diverted by man, 11.6 mgd is used for public supply and 44.4 mgd for industrial and private supplies. Diversions of streamflow furnish 86 percent of the public supply and 27 percent of the industrial supply, and ground-water sources yield the remainder. Municipal and private sewage treatment plants are upgrading the waste water in many places, but no provisions are being made for treatment other than natural dilution and assimilation for the 15 mgd of coal-nine drainage in the northern part of the basin. Technology for economic treatment of mine water is not available at this time, although research in this field is being done. Urbanization eastward from Harrisburg and around Lebanon has increased the population density of the basin. Densities of 500 people per square mile and water use exceeding 2.0 mgd per sq mi can be expected in the future. By the year 2000 the population of the basin may increase 60 percent; and if the per capita rate of use increases 0.5 percent per year the domestic requirements for water will be about two times the present use, or 23 mgd. Similarly, if the present 1:4 ratio of domestic use to industrial use of water continues, at least 89 mgd will be needed for industry in the future. Although an increase to twice the present use of water can be foreseen, or 112 mgd, water for the dilution and assimilation of wastes from treatment systems are not included. Providing water for dilution of wastes from treatment plants has not been a problem, but in the future the amounts needed for this purpose will be greater as the population increases. As water becomes more valuable, treatment of sewage wastes to reduce the biochemical-oxygen-demand load by at least 80 to 90 percent will be necessary to conserve water for more productive uses. As much as 100 mgd may be needed for waste dilution in the basin by year 2000. The present trends in suburban and light industrial development will probably persist in the basin. Problems arising through changes in economic value of water, conflicts in use, and alternatives in development are typical of those confronting the manager of a water-resource system.

Pennsylvania↗