Open Access. Powered by Scholars. Published by Universities.®

Earth Sciences Commons™

Open Access. Powered by Scholars. Published by Universities.®

Old Dominion University

Discipline
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 631 - 660 of 663

Full-Text Articles in Earth Sciences

Input And Distribution Of Sewage Derived Sedimentary Material Adjacent To Chesapeake-Elizabeth Sewage Outfall, Virginia Beach, Virginia, Robert Carroll Brown Apr 1983

Input And Distribution Of Sewage Derived Sedimentary Material Adjacent To Chesapeake-Elizabeth Sewage Outfall, Virginia Beach, Virginia, Robert Carroll Brown

OES Theses and Dissertations

The concentrations of coprostanol and hydrocarbons were measured in the effluent from the Chesapeake-Elizabeth sewage treatment plant and surface sediments from the area surrounding the effluent discharge site. Most of the coprostanol (>84%) and hydrocarbons (>91%) were associated with particulates in the effluent. Some of these particles were incorporated into the sedimentary column within the study area, while some may have escaped from the area.

The study area is found to be a dynamic area where changes in the percentage and distribution of fine-grained sediments occur over periods of months. The movement of fine-grained sediments is an important …


Cluster Analysis Of Grain Size Parameters From A Beach Ridge Complex, Cape Henry, Virginia, Amy T. Robbins, G. Richard Whittecar Jan 1983

Cluster Analysis Of Grain Size Parameters From A Beach Ridge Complex, Cape Henry, Virginia, Amy T. Robbins, G. Richard Whittecar

OES Faculty Publications

Cape Henry is a Holocene beach ridge complex at the mouth of the Chesapeake Bay. Analyses of cross-cutting relationships visible on aerial photographs divide the complex into five geomorphic zones. Low, arcuate beach ridges, ornamented in places with small dunes, characterize the four oldest zones. The youngest zone consists of large irregular-shaped dunes which bury the margins of all older zones. Locations of 102 samples taken from 1 m depths on ridge crests were based upon a random stratified sampling grid covering all of Cape Henry. The use of half-phi size data generated standard sediment parameters. Weighted-pair cluster analyses of …


A Pore Water/Solid Phase Diagenetic Model For Manganese In Marine Sediments, David J. Burdige, Joris M. Gieskes Jan 1983

A Pore Water/Solid Phase Diagenetic Model For Manganese In Marine Sediments, David J. Burdige, Joris M. Gieskes

OES Faculty Publications

A steady state diagenetic model is developed which accounts for changes in both the pore water and solid phase manganese profiles in marine sediments as a result of advection, diffusion, and redox reactions. The model is applied to observations on two cores in the E equatorial Atlantic in which pore water and solid phase manganese data are available. In situ reaction rates for manganese oxidation and reduction are estimated. The oxidation rates calculated here are in good agreement with rates measured in laboratory studies. In addition, the calculated manganese oxidation and reduction rates are compared with other estimated rates for …


The Marine Geochemistry Of Selenium, Kazufumi Takayanagi Oct 1982

The Marine Geochemistry Of Selenium, Kazufumi Takayanagi

OES Theses and Dissertations

A fluorometric method for the determination of Se (IV) and total selenium in natural waters has been developed and optimized. The detection limit is about 20 pM for both analyses using a one liter sample. The precisions were about 2 % at 338 pM for Se (IV) and at 234 pM for total selenium.

The concentrations of both total selenium and Se (IV) decreased with increasing salinity in the surface waters of the James River and southern Chesapeake Bay. While total selenium seemed to exhibit conservative behavior at salinities above 0.36 ('o)/oo, Se (IV) was apparently removed during estuarine mixing. …


Analysis Of Heavy Minerals In Arenaceous Lutites From The Northern Canada Basin, Arctic Ocean, Kim Zauderer Oct 1982

Analysis Of Heavy Minerals In Arenaceous Lutites From The Northern Canada Basin, Arctic Ocean, Kim Zauderer

OES Theses and Dissertations

Heavy minerals from arenaceous lutites in three widely spaced cores from the northern Canada Basin were analyzed for the first time to determine the provenance of these sediments. The abundant minerals (sp. gr. == 2.70) in decreasing order for most samples were detrital carbonate, micas, clinoamphibole, clinopyroxene, garnet, epidote, tourmaline, and chlorite. The majority of pyroxene grains were etched. Sedimentary sources dominated and metamorphic and igneous sources were important but secondary. The northern Canada Arctic Archipelago and northern Greenland is proposed as the provenance for the heavy minerals in the arenaceous lutites for at least the past three million years. …


The Effects Of Varying Fresh Water Discharge On Dispersion In An Estuarine Hydraulic Model Of The Lafayette River, Norfolk, Virginia, Michael J. Jugan Oct 1982

The Effects Of Varying Fresh Water Discharge On Dispersion In An Estuarine Hydraulic Model Of The Lafayette River, Norfolk, Virginia, Michael J. Jugan

OES Theses and Dissertations

Three experimental tests were conducted in the Lafayette River branch of the Chesapeake Bay Hydraulic Model, each successive test with an increase in the amount of fresh water discharged into the head of the river. This was done to study the response from varying river discharge on mixing parameters including the longitudinal dispersion coefficient (E).

The model generated a tide of constant range and period. Batch releases of Rhodamine WT dye were made in the model and sampled throughout the river for ten tidal cycles. Samples were taken simultaneously at selected high and low water slack.

The calculation of the …


Some Effects Of The Polychaete Nereis Succinea Frey And Leukart 1847 On The Distribution Of Copper Cadmium And Zinc In Sediments And Water, Gabriela Kitzig August Oct 1982

Some Effects Of The Polychaete Nereis Succinea Frey And Leukart 1847 On The Distribution Of Copper Cadmium And Zinc In Sediments And Water, Gabriela Kitzig August

OES Theses and Dissertations

Two laboratory experiments, each lasting 216 hours, were conducted in order to determine the effects of a burrowing polychaete, Nereis succinea Frey and Leukart, 1847, on the distribution of copper, cadmium, and zinc in sediments and water in environmentally controlled microcosms. Dissolved metal concentrations in microcosms containing worms (experimental) decreased more rapidly than in microcosms without worms (controls). From 72 hours to 216 hours, suspended metal concentrations in experimental microcosms increased while concentrations in controls remained relatively constant. Sediment cadmium concentrations in experimental microcosms increased more over time than in controls. Polychaetes accumulated significant amounts of all three metals. These …


Stratigraphy And Depositional Environments Of A Late Pleistocene Barrier Island Complex, Southeastern Virginia, Alan K. Jasper Jul 1982

Stratigraphy And Depositional Environments Of A Late Pleistocene Barrier Island Complex, Southeastern Virginia, Alan K. Jasper

OES Theses and Dissertations

The Norfolk, Kempsville, and Sand Bridge Formations beneath the HIckory Scarp of southeastern Virginia are reinterpreted as representing one glacio-eustatic transgressive cycle. The timing of this transgressive event is set during the earliest Wisconsinan. The formations were previously interpreted as unconformable overlying one another. The Norfolk-Kempsville unconformity is actually a diagenetic boundary. Evidence is presented which indicates that the Kempsville Scarp area should be reduced to member status or dropped entirely.


Geomorphology And Dynamics Of A Sand Wave In Lower Chesapeake Bay, Virginia, Gerardo Miguel Eduardo Perillo Jan 1981

Geomorphology And Dynamics Of A Sand Wave In Lower Chesapeake Bay, Virginia, Gerardo Miguel Eduardo Perillo

OES Theses and Dissertations

A single, more or less isolated, sand wave in a sand wave field recently discovered in the lower Chesapeake Bay, Virginia, was studied intensively for morphology, sedimentology and in terms of dynamic processes. The morphologic investigation consisted of bathymetric surveys of the sand wave field and the specific sand wave. Twenty-five grab samples and four box cores were obtained from different segments of the feature studied. Textural parameters of the samples were determined, and a multivariate technique was utilized to identify subenvironments on the feature. The box cores provided information on the internal structure of the sand wave.

Observations of …


The Distribution Of Cesium-137, Copper, Lead And Zinc In Various Sedimentary Environments Of The James River Estuary, Virginia, Colin Stevenson Moy Oct 1980

The Distribution Of Cesium-137, Copper, Lead And Zinc In Various Sedimentary Environments Of The James River Estuary, Virginia, Colin Stevenson Moy

OES Theses and Dissertations

Ten grab samples and eight cores were obtained within a short stretch of the James River estuary. The distribution of CU, Pb, Zn, Cs-137, organic carbon (TOC) and fine-grained sediments in various depositional environments were examined. Within the past quarter of a century, these measured parameters have been accumulating preferentially in the low energy environment (Burwell Bay). The inventory of Cs-137 in the cores was linearly related to the inventory of heavy metals and TOC. The concentrations of Cs-137 in the surface sediments vary linearly to those of the other parameters suggesting that Cs-137 may be used as a tracer …


The Effects Of Elevated Calcium Chloride And Magnesium Chloride Levels On Larval Growth And Survival Of Macrobrachium Rosenbergii (De Man) (Decapoda Palaemonidae) Reared In The Laboratory, James Thomas Michaels Ii Jul 1980

The Effects Of Elevated Calcium Chloride And Magnesium Chloride Levels On Larval Growth And Survival Of Macrobrachium Rosenbergii (De Man) (Decapoda Palaemonidae) Reared In The Laboratory, James Thomas Michaels Ii

OES Theses and Dissertations

The effects of elevated CaCl2 , MgCl2 , combination CaCl2 and MgCl2 concentrations and their associated ionic strengths on larval growth and survival of the freshwater prawn, Macrobrachium rosenbergii were investigated in the laboratory. Larvae were reared in diluted seawater of 15 parts per thousand salinity with elevated calcium concentrations of 330 parts per million and elevated magnesium concentrations of 1275 parts per million. Control larvae were also reared with elevated NaCl concentrations to duplicate the ionic strength increases of the combination CaCl2 - MgCl2 test solution which had the highest ionic strength. A …


Alkalinity And Ph In The Southern Chesapeake Bay And The James River Estuary, George T. F. Wong Jan 1979

Alkalinity And Ph In The Southern Chesapeake Bay And The James River Estuary, George T. F. Wong

OES Faculty Publications

The ranges of alkalinity and pH in the southern Chesapeake Bay and the James River estuary were 2.25 meq·liter−1 at 32‰ to


The Distribution Of Several Metals And Cation Exchange Capacity In Sediment Fractions From An Artificial And Natural Marsh, James River, Virginia, William Nivens Jul 1978

The Distribution Of Several Metals And Cation Exchange Capacity In Sediment Fractions From An Artificial And Natural Marsh, James River, Virginia, William Nivens

OES Theses and Dissertations

In order to examine the mechanisms by which Fe, Mn, Ca, Zn, Cu, Ni and Pb are bound in sediments, a sequential selective extraction procedure was employed on sediment samples collected at an experimental dredge disposal marsh and a neighboring natural marsh located near Windmill Point, James River, Va. The metal concentrations were determined in six phases, interstitial water, exchangeable, easily reducible (oxides of Mn), organic, moderately, reducible (oxides of Fe), and residual fractions. In addition, the cation exchange capacity (CEC) of the sediments was determined as well as the actual role of organics and colloidal iron coatings as they …


Suspended Matter And Light Attenuation In A Turbid Estuary, Daniel E. Campbell Oct 1977

Suspended Matter And Light Attenuation In A Turbid Estuary, Daniel E. Campbell

OES Theses and Dissertations

A study was made in Hampton Roads, Virginia, to characterize the suspended matter and to investigate its relationship to the light attenuation coefficient. The study gives a detailed description of the seston and its variations with time and space. An evaluation of the light attenuation coefficient as an indicator of seston distributional parameters was made.

The distribution of the suspended matter is obtained through gravimetric, Coulter counter and microscopic analyses. Microscopic analysis is employed to determine the composition of the seston and ATP determinations give the amount of living biomass. The suspended matter is characterized in terms of weight, numbers, …


Sediment Interstitial Dissolved Mercury And Carbon Relationships In An Artificial And Natural Marsh, James River, Virginia, Apostolos Katsaounis Jul 1977

Sediment Interstitial Dissolved Mercury And Carbon Relationships In An Artificial And Natural Marsh, James River, Virginia, Apostolos Katsaounis

OES Theses and Dissertations

Thirty six sediment cores were collected during August, 1976 and January, 1977 in order to examine the relationships between dissolved organic carbon and total dissolved mercury in the interstitial water of two marshes located near Windmill Point, James River, 16 km downstream from Hopewell, Virginia. The Windmill Point marsh development site is a dredged material disposal island in the James River. The reference marsh which does not contain dredged material, is located 2.3 km upstream at Ducking Stool Point.

The concentrations of dissolved organic carbon and total dissolved mercury showed no significant difference between the two marshes. Trends in the …


The Effects Of Dredging On The Stability Of An Ebb-Tidal Delta, Lynnhaven Inlet, Virginia, Donald Keith Riggenbach Oct 1976

The Effects Of Dredging On The Stability Of An Ebb-Tidal Delta, Lynnhaven Inlet, Virginia, Donald Keith Riggenbach

OES Theses and Dissertations

A channel was dredged in 1965 through the ebb-tidal delta of Lynnhaven Inlet, Virginia. The purpose of this study was to determine if this channel has affected the morphological configuration of the delta. It was proposed that the channel caused the dynamically stable delta to become unstable and change its morphology.

Bathymetric comparisons of seven surveys during the last 122 years, including one conducted during this investigation, show that prior to 1962 and the dredging operations, the delta had become dynamically stable. The present survey shows that the delta has changed its shape in response to the interaction of the …


Topography, Shallow Structure, And Sedimentary Processes Of The Atlantic Continental Slope Off The Carolina Coast, Robert Michael Fitchko Jul 1976

Topography, Shallow Structure, And Sedimentary Processes Of The Atlantic Continental Slope Off The Carolina Coast, Robert Michael Fitchko

OES Theses and Dissertations

Analysis of 58 closely-spaced bathymetric and seismic profiles of the Carolina continental slope from the northern Blake Plateau to the vicinity of the North Carolina-Virginia state line (latitude 32• 30 'N to 36• 30 'N) indicates sharp contrasts in quantity of slumping and outcrop ledge continuity.

Terrestrial progradation and a relatively gentle slope characterize the area south of Cape Lookout, especially between Cape Romain and Cape Fear where sediment mantling is the greatest. Submarine canyons, slumps, and a steep slope are characteristic Between Cape Lookout and Cape Hatteras. North of Cape Hatteras, canyons and slumps are also common, though sediment …


Stability And Local Effects Of An Offshore Sand Storage Mound, Dam Neck Disposal Site, Virginia Inner Continental Shelf, William Joslyn Saumsiegle Jul 1976

Stability And Local Effects Of An Offshore Sand Storage Mound, Dam Neck Disposal Site, Virginia Inner Continental Shelf, William Joslyn Saumsiegle

OES Theses and Dissertations

From 1967 to 1974 medium to coarse sand dredged from the Chesapeake Bay was stockpiled approximately three miles offshore of Dam Neck, Virginia in hopes that the sand could be recovered for local beach renourishment projects. The resulting mound was surveyed over a two year period to determine if the sand is being removed by wave and current action and if the creation of a new feature on the ocean bottom changes the wave refraction patterns and perhaps creates local erosion.

Bathymetric profiles across the storage mound show some apparent morphological changes, but a detailed analysis of this data is …


Control Of Clay Mineral Distribution By Estuarine Circulation, James River Estuary, Virginia, Jean-Pierre Feuillet Apr 1976

Control Of Clay Mineral Distribution By Estuarine Circulation, James River Estuary, Virginia, Jean-Pierre Feuillet

OES Theses and Dissertations

A study was performed on the clay minerals of the James River estuary, Virginia, to determine the predominant factors that influence clay mineral distribution in the estuary. The factors of differential settling, flocculation, and diagenesis show minor or no effects on distribution, while estuarine circulation exerts the strongest influence upon the clay mineral distribution.

There are two clay suites in the James River estuary. The upper James River clay suite is a kaolinite, dioctahedral vermiculite, and mixed-layer suite, with kaolinite being the major mineral. The lower Chesapeake Bay clay suite is an illite, chlorite, and montmorillonite suite, with illite being …


Dynamics And Sedimentology Of Inner Middle Ground - Nine Foot Shoal, Chesapeake Bay, Virginia, Mitchell Alan Granat Apr 1976

Dynamics And Sedimentology Of Inner Middle Ground - Nine Foot Shoal, Chesapeake Bay, Virginia, Mitchell Alan Granat

OES Theses and Dissertations

The historical, hydrodynamic, and sedimentological development of Inner Middle Ground - Nine Foot Shoal indicates that it is presently in quasi-equilibrium with mutually evasive ebb and flood tidal currents. Bathymetric comparisons among six surveys taken during the past 122 years depict development of the shoal from two linear sand bodies to its present double parabolic morphology. Circulation paths are proposed for each survey.

Information from eight current meter stations on and adjacent to Inner Middle Ground - Nine Foot Shoal were used to determine near-surface and near-bottom tidal current asymmetries and directions. The concepts of bathymetrically diverted currents and mutual …


Methane Distribution And Production In The Georgia Salt Marsh, Larry P. Atkinson, John R. Hall Jan 1976

Methane Distribution And Production In The Georgia Salt Marsh, Larry P. Atkinson, John R. Hall

CCPO Publications

Bacterial action in the anaerobic sediments of Spartina salt marsh produce large quantities of methane. Water in contact with the marsh has methane concentrations 200-300 times normal oceanic concentrations. The methane content of the water varies from maximum of 1.2 mu l CH sub(4)/ super(l) super(-1) in the summer to a minimum of 0.005 mu l CHl1


Processes Controlling The Distribution Of Methane In The Cariaco Tranch, Venezuela, Denis A. Wiesenburg Jul 1975

Processes Controlling The Distribution Of Methane In The Cariaco Tranch, Venezuela, Denis A. Wiesenburg

OES Theses and Dissertations

Abstract unavailable.


The Analysis Of Volatile Organic Compounds In The Southern Chesapeake Bay, Virginia By Gas Chromatography/Mass Spectrometry, James D. Haluska Jul 1975

The Analysis Of Volatile Organic Compounds In The Southern Chesapeake Bay, Virginia By Gas Chromatography/Mass Spectrometry, James D. Haluska

OES Theses and Dissertations

Sea-water samples from the Norfolk, Virginia area were analyzed for trace volatile organic compounds by helium sparging. Contents of the trap were injected into a gas chromatograph/mass spectrometer. Analysis of the trap contents indicated the presence of aliphatic and olef1nic hydrocarbons containing up to six carbon atoms and eight halogenated compounds of up to two carbon atoms in length. The halogenated compounds which were identified were dichlorofluoromethane, trichlorotrifluoroethane, carbon tetrachloride, chloroform, trichloroethane (2 isomers) bromodichloromethane, and chlorotrifluoroethylene. The

relative concentrations of volatile organic compounds generally tended to increase in samples collected from water prone to urban environmental pressures. All eight …


Heavy Mineral Distribution In The Lower Chesapeake Bay, Virginia, Frances Firek Apr 1975

Heavy Mineral Distribution In The Lower Chesapeake Bay, Virginia, Frances Firek

OES Theses and Dissertations

Heavy minerals from 195 bottom sediment samples of the lower Chesapeake Bay, Virginia have been studied. In comparison with other areas such as the Gulf of Mexico, qualitative and qualitative mineralogical variations were subdued, because of the absence of widely divergent source areas. The effect of present-day drainage system on the mineralogical distribution patterns is not clear, largely because of the complex Pleistocene history of the study area.

Seven geographic provinces were defined and treated statistically. An analysis of variance was conducted on the seven provinces. The more significant mineral species from the study area are zircon, hornblende, pyroxene, and …


An Investigation Of Littoral Transport Between Virginia Beach And Sandbridge, Virginia, Richard C. Cunningham Jr. Apr 1974

An Investigation Of Littoral Transport Between Virginia Beach And Sandbridge, Virginia, Richard C. Cunningham Jr.

OES Theses and Dissertations

A method for calculating littoral transport, direct determination of the sediment flux, has been proposed and evaluated. Three sampling stations, located between Virginia Beach and Sandbridge, Virginia, were occupied for a period of thirteen months (September, 1972 to September, 1973). Measurements include velocity of the littoral current, cross-sectional area of the surf zone, and in situ samples of suspended and bottom sediment load. Observations of sea and atmospheric conditions were obtained. Two ways of calculating littoral transport were derived from the same basic method, thus two sets of transport values were generated. Two annual littoral transport values were calculated by …


Evolution Of Platt Shoals Northern North Carolina Shelf: Inferences From Areal Geology, Philip C. Sears Oct 1973

Evolution Of Platt Shoals Northern North Carolina Shelf: Inferences From Areal Geology, Philip C. Sears

OES Theses and Dissertations

The evolution of Platt Shoals, a complex ridge and trough system on the south side of the Albemarle Shelf Valley, was determined and the modern hydraulic regime was inferred. The methods used were surficial grain size, 11 vibracores, seismic profiling and bathymetric maps. Platt Shoals developed in a three step process. The first, step was the formation of a substrate of late Pleistocene regressive deposits from 15,000 to 30,000 yr B. P. The second step, occurring approximately 11,000 yr B. P., was the formation of estuary mouth shoals of the ancestral Albemarle River. Between 4,4.00 to 5,000 yr B. P., …


Particle Size Distribution And Small-Scale Bed-Forms On Sand Waves, Chesapeake Bay Entrance, Virginia, John T. Wells Jul 1973

Particle Size Distribution And Small-Scale Bed-Forms On Sand Waves, Chesapeake Bay Entrance, Virginia, John T. Wells

OES Theses and Dissertations

The relationship between sediment texture and topography has been studied along five series of sand waves in Chesapeake Bay entrance, Virginia. Results indicate that two types of sand waves with reference to mean grain size are present: sand waves with coarse sediment on crests and fine in troughs, and sand waves with fine sediment on crests and coarse in troughs. Asymmetrical, migrating sand waves exhibit the first type; near-symmetrical, non-migrating sand waves exhibit the second type. In general, bimodal sediment is present on crests of migrating sand waves and in troughs of stationary sand waves. There is a progressive decrease …


Seismic Refraction Study Of Post-Pliocene Stratigraphy, Dismal Swamp, Virginia, William Brian Fraser Jan 1973

Seismic Refraction Study Of Post-Pliocene Stratigraphy, Dismal Swamp, Virginia, William Brian Fraser

OES Theses and Dissertations

This study examines Pliocene-Pleistocene lithostratigraphy and the Yorktown unconformity within the Dismal Swamp by means of remote sensing analysis, Wyrobek-Gardner seismic refraction profiling and split-spoon coring. Pre-Sangamon fluvial/tidal channel deposits are not present and the Yorktown unconformity dips irregularly southeastward at 0.35 meters/kilometer (2 feet/mile) from a high at 4 meters above sea level to a low of -1 meter (+12 to -2 ft) below sea level. The marker velocity for the Yorktown Formation is 1600 mps (5250 fps) and regression of seismic depths of the Yorktown Formation with corresponding split-spoon depths yields a high correlation. Short line upper layer …


Determination Of Nutrient Levels And Proposed Predictive Models For Phosphate In The Lafayette River, Norfolk, Virginia, John R. Montgomery Jul 1972

Determination Of Nutrient Levels And Proposed Predictive Models For Phosphate In The Lafayette River, Norfolk, Virginia, John R. Montgomery

OES Theses and Dissertations

The Lafayette River, an Urban, well-mixed estuarine embayment, was sampled from October, 1970 to January, 1972 for phosphate, nitrate, nitrite, oxygen, water temperature and salinity. The mean values found for these samples were: oxygen saturation from 69% to 106% nitrate from 0 to 4 microgram-atoms per liter, and salinity from 13 ‰ to 24 ‰. The mouth of the Elizabeth River to Hampton Roads as also sampled from May, 1971 to August, 1971. The Lafayette and Elizabeth Rivers were also sampled over a 24 hour period in the summer of 1971 and the Lafayette River again in the winter of …


An Evaluation Of A Stable Isotope Of Dysprosium For Labeling And Tracing Sedimentary Particles, Charles Glenn Boone Oct 1971

An Evaluation Of A Stable Isotope Of Dysprosium For Labeling And Tracing Sedimentary Particles, Charles Glenn Boone

OES Theses and Dissertations

An evaluation of the application of dysprosium oxide as a tracer coating to surface label sedimentary particles is made. Physical and chemical properties of the labeled sand are studied. Effective diameters and settling properties of the tracer sand are compared with unlabeled sand. A total of 8.51 kg of labeled sand was placed on the beach at Camp Pendleton. Dispersal patterns obtained 1 and 4 hours after tracer injection indicate a general down current mean tracer migration rate of 0.21 cm/sec (0.42ft/sec). An absolute detection limit of 4 or 5 parts per 100,000 and a real detection limit, after field …