Nitrogen Dynamics in Natural Systems Impacts of Onsite...

Nitrogen Dynamics in Natural Systems

Impacts of Onsite Wastewater Treatment and Dispersal Systems / Drip Dispersal

– Tom W. Ashton

Environmental Health Specialist

Professional Soil Scientist

April 6, 2016

Denver, CO

Executive Order 13508 of May 12, 2009

Chesapeake Bay Protection and Restoration

Virginia Department of Health, December 2013, Webinar Training, Implementing the Chesapeake Bay Nitrogen Requirements in the AOSS Regulations, Presented by Dr. Marcia J. Degen P.E., Office of Environmental Health Services

Phosphorus (Freshwater) & Potassium •No gas phase in cycle

PLANT and ENVIRONMENTAL NUTRIENTS

Nitrogen (Salt Water) •Multiple Biologic Pathways

•Created (Manufactured) / recycled

CHES Bay NITROGEN Loadings

On Site Septic 4%

AG Related 41%

Non AG 10%

Natural 1%!!

Atmospheric

Deposition 26%

CLASSICAL MODEL

•Efficient, closed system, small footprint. Employs fast-growing bacteria, short Mean Cell Residence Time (MCRT <20 days)

•Growth Media is often suspended (water)

•Basis is in surface water resource discharge

*Nitrify to protect aquatic organisms

*Denitrify to reduce the nutrient load on the water resource

Treatment Efficiencies

Discharge is primarily soluble, mobile NITRATE

Wetlands, Soils, and Sediments have many alternative pathways for NITROGEN transformation •Slow Growing Bacteria

•Extended MCRT (200 days?)

•“Low fluid shear” environment resulting in stable biofilms

•Time

•Size

•Diversity

The Classical Theory is no longer valid as a general model with applied to complex natural systems such as sediments, soils, and wetlands.

“CLASSICAL”

DeNite Pathway

DENITE

of

Nitrite

DENITE

of Ammonia

ANAMMOX •Nitrite and Ammonium to atmospheric Nitrogen

•Does not require organic Carbon to remove Nitrogen from Wastewater

•Removal high once biomass is established

•20% of Oxygen compared to classic Nitrification / denitrification

Ammonia to N gas by way of ANAMMOX

HETEROTROPHIC NITRIFICATION

MODEL

•Complex

•Uses Oxygen and Nitrate simultaneously as terminal electron acceptors favoring aerobic denitrification

“Dumps” excess ammonia to prevent interference with bacterium energy balance

Biofilms and “flood and drain” an important element

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FIRST VERSION AUGUST, 2013

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WHAT IS A BEST MANAGEMENT PRACTICE (BMP)?

** Basis, design concept as a natural system

** Accepted, engineering practice

** Specific criteria

** Robust / sustainable

** Applied and accepted as “deemed to comply”

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NSF 40 10 / 10

NSF 245

Majority of Application #5

NSF 245

21 21

<12” BGS

Traditional Prescriptive LPD, Elevated Sand Mound, and “At-Grade” are non proprietary public domain design methodologies

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TREATMENT TRAIN COMBINATIONS

NSF 40 and 10 / 10

NSF 245

NSF 245

Majority of Application NSF 245

Conventional Gravity Drainfield

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3.9 SHALLOW-PLACED PRESSURE-DOSED DISPERSAL

** Twelve papers cited.

** Seven Papers Specific to Drip Dispersal

FIRST VERSION AUGUST, 2013

** Two additional papers reflect “controlled application” at trench bottom loading rates. Instantaneous dose volume and frequency only achievable in field application with Drip Dispersal.

Anderson, Otis, Apfel

(six doses per day, .125-.25 gallons per dose.)

Duncan, Reneau, Hagedorn (six doses a day, . 083 gallons per dose.)

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Graphic from “L.D. Hepner Alternative On-Lot Technology Research / Soil Based Treatment Systems (Del-VAL Phase 2)”

Drip in situ vs. LPD interface

DRIP PLACES EFFLUENT INTO THE NATURAL SOIL SYSTEM

NOT ON TO A CONSTRUCTECTED INTERFACE

25 25 Macropores

Bt Horizon

Trench bottom

DRIP DISPERSAL IS NOT A TRENCH

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Drip Dispersal Vs. Low Pressure Pipe

• Direct burial vs. trenches • Area loading (gal./ft.2) equivalent to LPD • Linear loading (gal./ft. of pipe)

– 10 to 12 times less than LPD • 8 to 10 times more orifices than LPD • Drip Flow 5%-8% per orifice • Total Drip Dose Volume 10% to 20% of LPD

volume

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How Does Drip Treat? THE SOIL TREATMENT UNIT (STU)

THE Drip “Bio-Reactor”

.01 GPM

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** DESIGN Absorption Area footprint by and large equivalent to conventional LPD STE trenches

** DESIGN Enhanced tubing “Line Loading” interface for maximum soil contact

NITROGEN

Size and Time

Drip and the “Soil Treatment Unit” (STU) ** Heterogenious biological environment in shallow soils, maximum activity

** Free gas exchange (aeration)

** Primarily unsaturated conditions provide extended effluent residence time for treatment

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How Does Drip Treat? EXCELLENT DISCUSSIONS

LONG Long, T. 1995. “Methodology to Predict Nitrogen Loading from On-Site Sewage Treatment Systems”. In Proceedings of the Northwest Onsite Wastewater Treatment Short Course, ed, R.W. Seabloom. University of Washington, Department of Civil Engineering, Seattle, Washington, September, 1995.

NOWRA MODEL CODE Del Mokma, draft report “Soil Treatment of Onsite Wastewater: Basis for Determining Constituent Output for Soil Component Matrices of National Model Code” sponsored by NOWRA National Model Code Subcommittee on Soils, Jerry Tyler, University of Wisconsin and Del Mokma, Michigan State University.

WALLACE Wallace, Scott 2008 “Emerging Models for Nitrogen Removal in Treatment Wetlands” Scott Wallace P.E, M.S., North American Wetlands”, David Austin, P.E., M.S., Principal Technologist, Natural Treatment Systems, CH2M HILL, Journal of Environmental Health, Volume 71 Number 4, Fall 2008, National Environmental Health Association, Denver, CO.

31 Likely the most exhaustive characterization of the soil treatment unit (STU) to date. 670 total pages.

DRIP DISPERSAL

The Soil Treatment Unit (STU)

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•Examination of 120 sources with 25 sources containing 85 peer reviewed experiments. For the most part all studies apparently reflected domestic strength STE, single family home application & lab studies. •In many cases the authors had to make educated adjustments and assumptions to fill in missing data in order to generate a data set for analysis. These adjustments were based on an extensive review of the literature. The majority of studies were in Group I, sandy soils.

TEXTURE

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* LAB STUDIES Control on the part on the researcher regarding the amount and method of application as opposed to variable flow and application in situ.

*FIELD STUDIES Analysis attributed 66% of the variance in N attenuation to Hydraulic Loading Rate (HLR), 20% to depth, 3% to soil textural class, and 11% to the variability within the data itself.

* For lab studies the soil type was the most important factor, followed by depth, and then followed by HLR . Apparent lesser importance of soil parameters in field studies was attributed to the great variability in soil properties, even within a particular soil type at field sites. These results point to the complexity in which different STU factors impact N treatment.

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•Given the variability and scarcity of data collected in field sites, it is unlikely that field data can be used to predict N attenuation for many relevant Onsite Wastewater Treatment Systems (OWTS) and STU operating conditions. Mathematical models are needed that incorporate relevant design variables and operating conditions.

•HLR may be more important to N treatment within the first 30-60 cm than soil texture and soil depth. Soil depth and soil texture remain important variables. Soil structure may bear out to have a greater effect than soil texture.

Thus the subsequent document by the same team “Quantitative Tools to Determine the Expected Performance of Wastewater Soil Treatment Units” (WERF. 2010). STUMOD, NCALC, & HYDRUS

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“……HYDRUS was modified to account for the effect of water filled porosity, carbon content, and temperature on treatment to improve its ability to simulate nitrogen transformation under a variety of OWTS loading conditions “

.095 gal/ft2/Day

.076 gal/emit/Dose

60+ mg/l total N

<20 mg/l total N @ 30 cm

NO3- H20

“Tool Kit”

“For drip dispersal systems, the HLR is a function of the frequency and duration of doses each day for a given length of dispersal tubing…”

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•Nitrate removal increased over 66% in a drip field with a relatively low hydraulic loading.

•In general the model predicts that N applied by drip dispersal greatly influences the soil environment at a depth close to the emitter, but with increasing depth the influence of wastewater nitrogen decreases.

HYDRUS computer modeling of drip dispersal performance was conducted in a variety of loading rates, dosing regimes, and soil conditions.

•Two factors were identified as having the greatest impact minimizing the deep leaching of NO3

- are finer soil textures and a lower application rate.

•The long residence time in the soil column with subsurface drip enhances the opportunity for denitrification.

37 R.A. Beggs, 2004 MODELING SUBSURFACE DRIP APPLICATION OF ONSITE WASTEWATER TREATMENT SYSTEM EFFLUENT R. A. Beggs1, G. Tchobanoglous2, D. Hills3, and R. W. Crites4

HYDRUS MODEL Loading Rate LOW .1 gallon Ft2 per day HIGH .4 gallon Ft2 per day

Lower HLR

Increased

Residence

Time

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A Hydrus 2D vadose zone model with nitrification and denitrification rate coefficients calculated as a function of soil moisture content fit the container test results reasonably well. Model results were sensitive to the denitrification rate moisture content function. The greatest nitrogen losses (30 to 70%) were predicted for medium to fine texture soils and soils with restrictive layers or capillary breaks.

BOUNDARIES

Container tests were performed to determine the fate of water and nitrogen compounds applied to packed loamy sand, sandy loam, and silt loam soils. Nitrogen removal rates measured in the container tests ranged from 63 to 95% despite relatively low levels of available carbon.

Impact of Bacteria & Dosing Frequency on the Removal of Virus within Intermittently Dosed Biological Filters Robert Emerick, Ph.D

JaRue Manning, Ph.D

George Tchobanoglous, Ph.D

Jeannie Darby, Ph.D

The higher the loading rate, the more smaller doses per day required to maintain unsaturated conditions, lower field capacity.

18 Doses

50% Field Capacity

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All American PERC-RITE® STE drip dispersal system studies studies were performed in the Mesic soil temperature regime, with two (Colorado School of Mines and the University of Wisconsin) proximate, partially within, the frigid soil temperature regimes.

IN-SITU STE DRIP DISPERSAL

The Chesapeake Bay watershed lies within the Mesic soil temperature regime in the northern and western portions with the tidal portions of Virginia primarily in the Thermic soil temperature regime.

CSM

DELVAL

DNREC

U of MO

U of WI

U of TN

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DEL VAL 400 GPD .17 GPD per ft2

INFLUENT

43.94 mg/l TOTAL

NH3-N NO3-N

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DEL VAL MEDIAN DATA 12”

6.57 mg/l TOTAL NH3-N NO3-N reduced from 43.94 mg / L

85%

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IN-SITU STE DRIP DISPERSAL Both studies sampled above, within, and below single family home drip dispersal systems. Soils Somewhat Poorly Drained to Moderatelly Well Drained. Shallow to seasonal water tables / restrictions. Significant Nitrogen reductions. J. G. Hayes Jr. 2007, “Long Term Impacts of Micro-Irrigation “Drip” Treatment and Disposal Systems on Delaware’s Marginal Soils”

Coarse Loamy Mid-Atlantic Coastal Plain soils. Two phases (8 years) Four sites, three STE. Total nitrogen in the septic tank effluent averaged 54 mg/L.

Sievers, D.M.,Miles, R.J., 2000. “Final Report—Rock Bridge Onsite Demonstration Project”.

Fine Loamy (SiCL) / Clay soils, Karst topography, Columbia MO. One site. Area loading rate of .125 (peak design flow) and .044 gal/ft2/day (average). Effluent TKN 34.4 – 44.5 mg/L.

All results <10 mg/L

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Parzen 2007 Controlled Field Performance Evaluation of a Drip Dispersal System Used for Wastewater Reclamation in Colorado R.E. Parzen, J. Tomaras, R.L. Siegrist (Colorado School of Mines, Golden, CO), Eleventh Individual and Small Community Sewage Systems Conference Proceedings, 20-24 October 2007, (Warwick, Rhode Island, USA)

“The purpose of this study was to develop a method for the evaluation of nitrogen movement and fate in the STE applied to soil through subsurface drip dispersal systems. Nitrogen isotope and bromide tracers were added to a drip system at the CSM test site…..After tracer additions, soil and vegetation samples were collected in 3-D space in relation to the drip tubing emitters 2-4 days after tracer application.”

COLORADO SCHOOL OF MINES

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STE effluent dispersed five times a day at footprint loading rates of

.12 G/ft2/d) for Zone 1 and .24 G/ft2/d for Zone 2. STE Effluent TN average 72 mg/L

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Effluent water dispersed from an emitter infiltrates at the emitter and along the drip tubing and water movement is influenced by hydrologic conditions.

Based on precipitation and evapotranspiration at the Test Site, only a portion of the effluent water dispersed migrated downward in the soil (approx. 34% or 64% for Zone 1 or 2, respectively).

Sampling within Zone 1 revealed water filled porosities were high throughout the soil profile (>85%) and water content was most elevated along the drip tubing (22% dry wt.), which is also where soil pH was most depressed (pH 4.5) due to nitrification reactions.

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Six systems were studied, three of which were American Manufacturing Perc Rite® Drip Dispersal systems utilizing septic effluent. Extensive soil temperature monitoring. Despite a high background measurements, Nitrogen levels for Nitrate and Ammonium were found to be comparable with depth to back ground levels with the authors suggesting no significant increase in Nitrogen levels in the soil due to the addition of wastewater.

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ABSTRACT “Two subsurface drip irrigation (SDI) systems were installed and monitored at two sites in Tennessee. These locations were residential developments each served by a septic tank effluent pump (STEP) collection system, a recirculating media filter (fine gravel media), and SDI dispersal. At both locations, SDI research plots were established to receive primary treated (septic tank effluent) and secondary treated (recirculating media filter effluent) wastewater. In close proximity to randomly selected SDI emitters, soil samples were extracted…. Results indicate that the primary-treated side had lower hydraulic conductivity values, higher nitrate and higher total nitrogen levels than the secondary-treated side and the background soil…”

“The primary effluent application site showed a decrease in concentration for all constituents with increased depth. Secondary treatment does result in a higher quality effluent but is not needed when applying effluent with a SDI.”

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The fields were loaded at .1 gal/ft2/d. Tubing was installed at 6”. One site was a clay loam soil the other a sandy loam soil.

The STE effluent total nitrogen was in the typical range or 40 – 45 mg/L (personal communication with Tom Ashton May 2011).

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CONCLUSION “The purpose of this study was to evaluate two strengths of wastewater (STE and RSFE) being applied by SDI to determine the need for secondary treatment. The purpose was not to evaluate the performance of SDI as a whole. SDI augments the soil’s ability to treat wastewater but its full potential may be diminished by the use of secondary treatment. Physical and chemical properties of the soil were measured to make the comparison. It was found that the pore water in the soil that had been irrigated with the low strength wastewater (RSFE) was of slightly higher quality than the pore water in the STE side.“

“The benefits of a secondary treatment are not significant enough to make it necessary when using a SDI. The soil provides much of the same treatment as a pre-treatment system, and SDI dispersal systems are designed to fully utilize these characteristics.”

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Graphic from “L.D. Hepner Alternative On-Lot Technology Research / Soil Based Treatment Systems (Del-VAL Phase 2)”

Drip in situ vs. LPD interface

DRIP PLACES EFFLUENT INTO THE NATURAL SOIL SYSTEM

NOT ON TO A CONSTRUCTECTED INTERFACE

52

Trench Soil Treatment Low Pressure <12”

Application Depth

12” Vadose

Zone AEROBIC

“Micro” Sites

BOUNDARY CONDITION Minimum 12” AEROBIC Vadose Zone necessary for Nitrification

and Hydraulic Dispersion

DENITRIFICATION

Shallow BOUNDARY CONDITION creates conditions of soil at or near saturation,… assuming adequate Organic Carbon……. DENITRIFICATION

Microsites (hot spots) have variable moisture, gaseous, and environmental conditions (C) favorable to NITRIFICATION and DENITRIFICATION

2’ wide 2’ wide 2’ wide

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DRIP DISPERSAL DYNAMICS

Middle value of typical Dose Volume per Emitter .09 - .25 gallons

8” Diameter SPHERE of Influence MACROPORE VOLUME .28 gallons

60% MACROPORE VOLUME .168 gallons

8”

•Porosity refers to that portion of the soil that is not occupied by solid material (mineral or organic).

•Porosity is a function of texture and structure of the soil.

• Porosity has a direct influence on gas exchange (aeration), infiltration of water, and movement of water through the soil profile.

•Soil pores represent 50% of the volume, can be air filled (macro pores) or water filled (micro pores). Saturated flow occurs through macropores, 25% of the volume. Unsaturated flow occurs through micro pores.

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DOSE / DENITRIFICATION

Emitter and Tubing Line Load N GASES

6-8” Application Depth Maximum Organic

Carbon

“Micro” Sites

BOUNDARY CONDITION

Saturated Porosity 15 minutes+ ANAEROBIC Conditions, dose delivery .01 GPM, >60% water filled porosity

DENITE

“Line Load” provides relief along tubing when exceeding the instantaneous soil dose.

DE NITE

DENITE

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RESTING / NITRIFICATION

Emitter and Tubing

Unsaturated zone 6-8” Application Depth

12” Vadose Zone

AIR

“Micro” Sites

BOUNDARY CONDITION

Unsaturated zone

Rest time between doses typically 3 – 6 hours

NITRIFICATION

NITRIFICATION

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DOSE / DENITRIFICATION

Emitter and Tubing Line Load N GASES

6-8” Application Depth Maximum Organic

Carbon

“Micro” Sites

BOUNDARY CONDITION

Saturated Porosity 15 minutes+ ANAEROBIC Conditions dose delivery .01 GPM, >60% water filled porosity

DENITE

“Line Load” provides relief along tubing when exceeding the instantaneous soil dose.

DE NITE

DENITE

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SUMMARY STATEMENTS

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SUMMARY STATEMENTS

Natural Soil Conditions

** Soils are natural bodies and represent a multivariable continuum diverse in biological processes. Soil processes are central to the global nitrogen cycle representing a large portion of nitrogen transformation.

** The maximum zone of biologic activity and diversity is in the surface horizons of the soil. The environment is dynamic in its interaction with, in response to, plants, precipitation, the atmosphere, and parent material weathering.

** Reaction rates of nitrogen compounds in the soil are generally rapid with the the appropriate conditions (presence of the reactants / soil environmental conditions).

** In addition to the classical wastewater amonification / nitrification / denitrification process applied in wastewater treatment, soils present an environment conducive to a multitude additional pathways of nitrogen cycle in nature.

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SUMMARY STATEMENTS Optimize Gas Exchange ** By way of soil texture, structure, and porosity, the shallow soil horizons have adequate conditions for gas exchange within the medium and with atmosphere. Gas exchange with the atmosphere decreases with soil depth below ground surface. Shallow soils have various conditions of moisture status within the medium providing dynamic aerobic, facultative, and anaerobic conditions in close proximity.

** The major limitation for nitrification is oxygen. In favorable soil moisture conditions, soil air O2 in the shallow soil horizons is adequate for nitrification.

** A 12” soil depth vadose zone is recognized as adequate to provide nitrification.

Absorption ** The positively charged Nitrogen ions in septic tank effluent are readily absorption to soil solids at rates reflected by clay content and type. Adsorption varies by orders of magnitude from low in sands to very high (6x) in clays. Nitrogen cations are available for use by biological life (microbes and plants) with the remaining likely eventually nitrified within a few days.

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SUMMARY STATEMENTS

Carbon ** Soil air CO2 in shallow soils is adequate for nitrification. The biological treatment of applied STE effluent BOD provides additional CO2 to assure the demand is met.

** The major limitation in denitrification is organic carbon. Surface horizons have the highest amount of organic carbon available for denitrification. STE effluent BOD provides additional carbon to meet the demand.

** The minimum carbon to nitrogen (C:N) ratio to facilitate denitrification is in the range of 4:1 to 7:1 depending on the form of carbon. If the C:N ratio is lower than 4:1, then sufficient carbon may not be present for denitrification. For residential STE, the C:N ratio is likely within the range of 4:1 to 7:1.

** Alternatively, for nitrified effluent if the carbon is reduced and nitrate-nitrogen remains high, these conditions may limit subsequent denitrification.

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SUMMARY STATEMENTS Additional Mechanics ** Natural factors necessary for the process of nitrification, denitrification include the need for alternating aerobic / anoxic environments, and equal distribution across the entire infiltration surface providing low velocity film flow.

Differences in soil texture, structure or drainage class affect nitrification / denitrification, largely through the presence of adequate oxygen, organic carbon and the soil water content.

** Conditions beneficial to denitrification occur when the soil pores are at least 60% saturated, or when the soil air contains no more than 10% oxygen.

** Denitrification may also occur also in well-aerated soils, in anaerobic microsites and through other “non-traditional” pathways.

** Soil column biofilm “micro sites” provide variable moisture and oxygen status.

A low fluid velocity environment provide for facultative biofilms that are very stable.

This dual (air and water-filled) soil porosity is maximized with drip dispersal.

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The Soil “Bio-Reactor”

Nitrogen Dynamics in Natural Systems

Impacts of Onsite Wastewater Treatment and Dispersal Systems / Drip Dispersal

– Tom W. Ashton

Environmental Health Specialist

Professional Soil Scientist