SUBSURFACE DISTRIBUTION OF NITRATES BELOW COMMERCIAL CATTLE FEEDLOTS, TEXAS HIGH PLAINS

VOL. 7, NO. 5 WATER RESOURCES BULLETIN OCTOBER 1971

SUBSURFACE DISTRIBUTION OF NITRATES BELOW COMMERCIAL CATTLE FEEDLOTS, TEXAS HIGH PLAINS’

William D. Miller‘

ABSTRACT. Samples for water-quality analyses were collected from beneath eighty commercial cattle feedlots in the Texas High Plains. Twenty-two feedlots were drilled and/or cored to establish vertical gradients of dissolved solids. Sample and gamma logs, size analyses and vertical permeability of cores were determined from samples beneath these lots.

Relationships of groundwater saturated thickness, depth to watertable, and age of lots to specific- ion distribution were evaluated. The study includes lots ranging in age from 35 years to new installa- tions. Runoff collection-systems on lots include playas, man-made ponds, and dammed and undammed stream channels.

Infiltration of feedlot liquid waste to the watertable below feedyards is insignificant in most localities in the Texas High Plains. Infiltration of “collected” feedlot runoff and subsequent concentration of dissolved ions in groundwater in the High Plains are dependent upon, among other things, (1) surface and subsurface geology, (2) depth to water, (3) thickness of the groundwater zone, and to (4) differences in lateral and vertical permeabilities of the Ogallala Formation, the major aquifer.

Certainly, no regional subsurface pollution problem exists today nor is one foreseen from cattle feedlot runoff in the Texas High Plains. (KEY WORDS: nitrates; groundwater; Ogallala; cores; permeability; geologic environment)

INTRODUCTION

Speculation has been rampant for several years concerning the pollution hazard of commercial cattle feedlots to the groundwater zone (Ogallala Formation) of the Texas High Plains. A part of this study has been devoted to developing field and laboratory data relative to the question of how significant is the speculative “pollution hazard.” Major objectives of the investigation include the following: (1) determination of quantitative distribution of nitrogen (NO,, NO,, NH,, Org-N) and other chemical parameters (Ca, Mg, Na, K, C1, SO4, pH, TDS) in cores and in groundwater below major feedlots, ( 2 ) evaluation of field and laboratory determined rates of nitrate movement from surface to watertable, (3) determining time-space distribution of ions in the saturated zone, and (4) the determination of what geologic environ- ments in the High Plains are least conducive to infiltration of cattle feedlot runoff.

Data collected for the total study include information on cattle feedlot location, load history, age, runoff-collection systems (geometry, gradient, types, capacity, use, water chemistry), and subsurface geology (stratigraphy, core chemistry, mineralogy, size distribution, vertical permeability). This report is based on information from field and laboratory investigation of 80 cattle feedlots (location, Figure I) , ranging from new to 35 years in established

‘Paper No. 71083 of the Water Resources Bulletin (Journal of the American Water Resources Associa- tion). Discussions are open until April 1, 1972. Portions of this work were performed pursuant to contract no. 14-1 2-804 with Environmental Protection Agency. Also, funding was received from Texas Water Development Board, Texas Cattle Feeders Association, North Plains Water District (Texas), and Texas Tech University .

‘Professor and Chairman, Department of Geosciences, Texas Tech University, Lubbock, Texas 79409. Lubbock, Texas 79409.

94 1

942 William D. Miller

41LEY LAMB , 1 .-A

\

m

xm*N HOCKLEY LUBWCK

Fig. 1. Location of cattle feedlots investigated in study, Texas High Plains.

NITRATES BELOW COMMERCIAL CATTLE FEEDLOTS 943

age (distribution, Figure 2), and with a one-time cattle load of over one million head (load vs year established, Figure 3).

Space does not permit reporting on all facets of the p r ~ j e c t , ~ therefore we will address the questions of (1) what factors are related to subsurface distribution of nitrate below feedlots, and (2) is there significant nitrate seepage beneath cattle feedlots in the Texas High Plains?

10

9

8

r 7 s E 6

k 5 Y Y

m g 4 3 z

3

2

1

0 51950 51 52 53 54 55 56 57 58 59 1960 61 62 63 64 65 66 67 68 69 1970

Fig. 2. Age distribution of feedlots in study.

Fig. 3. Approximate average cattle load vs year feedlot established.

3See report by EPA, Water Pollution Control Research Series (16060 EGS 01/71), entitled, Infiltration Rates and Groundwater Quality Beneath Cattle Feedlots, Texas High Plains.


PERTINENT HIGH PLAINS GEOGRAPHY-GEOMORPHOLOGY

Cattle feedlots are concentrated in high yield feed-grain areas which in turn are related to high yield groundwater zones and to regional soils patterns. These three fortuitously inter- related factors have led to development of cattle feeding as a major industry for the Texas High Plains.

Feedlots are ordinarily located on stream drainage systems or playa systems. In this study, approximately 40% of the feedlots are located on streams, 45% on playas and 15% have no relation to the aforementioned geomorphic features. Of course, good drainage is an economic asset and usually such benefits are readily obtainable by proper geographic location.

High Plains streams have gradients varying from about 10 feet/mile to usually less than 5 feet/mile. Feedlot playas in this study have a relief of 5 to 45 feet of closed contours. Feed- pens located on sides of stream channels and playas in Armstrong, Bailey, Castro, Lamb, Lubbock, Parmer and parts of Deaf Smith counties (Figure 1) have drainage slopes of 2% to 5%. Feedpens in Floyd, Hale, Gray, Potter, Oldham and Moore counties have slopes between 0.2% and 2%. Rarely do feedpen slopes of this region exceed 5% in value.

Soils distribution in the Texas High Plains (Figure 4) has a significant relation to infiltration of surface water, thus a relationship to infiltration of cattle feedlot runoff. Rates of infiltration and total accumulation of dissolved solids from feedlots are generally higher in “sandy soils” and areas of “sand dunes” than in tighter soil-zone areas. As stated, this is true for all forms of filtrate whether from feedlots or other sources. Total-dissolved-solids (TDS) and specific-ion maps (chloride, nitrate)4 of areas where no feedlots are located clearly indicate this relationship. Groundwater is naturally higher in dissolved solids in the “sandy” zones than in “tighter” soil areas, and was before and will be after further cattle feedlot development. A contributing factor for the sandy soils, groundwater -quality relationship is the relatively rapid entrapment of surface water by loose surficial material which prevents ready runoff, evaporation, and even evapotranspiration due to low plant density. One should add that the significance of soils distribution in terms of potential degradation of large volumes of groundwater is diminished when one considers the low total number (k20) of feedlots in the sandy soil zones of the High Plains.

SURFACE AND SUBSURFACE LITHOLOGY

The surfacing materials on stream and playa feedlot slopes usually (290%) consist of dense, fine-grained, semi-consolidated soils underlain by caliche. Feedlots located on Texas High Plains streams have feedpens situated on slopes consisting of caliche and thin soils, but often the stream bottoms (where runoff collects) have breeched the caliche. Feedlots in headwater areas and tributaries of streams have the usual caliche zone beneath the stream channel. Stream channels drilled in this study that have breeched the caliche are floored by poorly permeable, thin (?I-lo’) zones of clayey silt, and underneath this almost always underlain by a thin zone of fine to coarse-grained sand and/or gravel. The clayey silt and sand-gravel valley- fill overlie the Ogallala Formation.

Though all our permeability data are not complete, vertical constant head permeability values thus far determined for the clay-silt sediments of valley fill are cm/sec or less. The underlying sand zones usually have vertical permeability values of cm/sec or larger.

4Derived from published and unpublished data of Texas Water Development Board, High mains Water District and North Plains Water District.


0 FINE TEXTURED SOIL4

SANDY SOILS

SAND DUNES

Fig. 4. Generalized soil texture map, Texas High Plains [after Carter, 1931; Lotspeich & Coover, 1962; Lehman, Stewart & Mathers, 19701.


The “pond” of a playa is almost always surfaced by a layer of clay. The clay zone is underlain by layers of “lakefill” sand and/or lenses of clay-silt-sand. Playa “fill” has been measured up to 23 feet in thickness, and is always underlain by the Ogallala Formation. Vertical permeability values of playa lake clay are to 10’ cm/sec or lower in value (impermeable).

Surficial silt-clay mixtures surfacing feedpens and/or runoff slopes exhibit secondary cementation in the form of root fillings, vug and pore fillings, and veinlets. Below this developed hardpan, soil densities are noticeably less and permeability values are larger. Vertical constant head permeability values typical of the hardpan surface of feedpens and drainage slopes are lo-’ to l o 7 cmlsec. Caliche below playa and stream channel collection systems is porous and permeable. Secondary solution of caliche is evidenced by vugs, secondary cementation of fractures and solution vugs, and by silt-clay filling in solution vugs and voids. Lithification of medium and coarse-grained clastic zones is noticeably absent directly beneath the “standing water area” (pond) of all types of collection systems.

The Ogallala Formation underlies the surficial material at all sites drilled in this study. We have noted that Ogallala lithology is often misrepresented in literature in terms of sediment size-distribution, particularly in the Southern High Plains. Usually the unit is described as a silt, sand, and gravel sequence. The bulk volume of gravel in the Ogallala is a small percentage of the total sediment volume. The mistaken identification of gravel commonly comes from drillers logs and outcrop observations. In lieu of gravel, the gravel-size material noted in driller logs is often cuttings of rock fragments, the rock fragments being cut from nodular and lense-shaped cemented zones of fine- to medium-grained quartz sand so common to the Ogallala Formation. The apparent gravel percentages represented on outcrop often are enhanced by winnowing of loosely consolidated clastics.

In terms of infiltration, laboratory determined permeability values in the unsaturated zone usually vary from cm/sec to l o 6 cmlsec. The larger permeability values of Ogallala sediments will permit rapid percolation of water. Of course, minimum permeability of near- surface material and minimum permeability values of Ogallala sediments determine practical transmissibility rates.

GROUNDWATER DISTRIBUTION

Groundwater is ubiquitous within the Ogallala Formation of this study. Depth-to-water ranges from a minimum of +lo feet (Tierra Blanca Draw) to depths of 250-300 feet in the study area. Saturated thicknesses vary from 30 feet to 300 feet in areas investigated. Within certain geographic locals, saturated thickness and/or depth to water are related to the occur- rence of nitrate and other dissolved solids in groundwater.

Generally, thin saturated zones have high nitrate concentrations. This generality is enhanced some by the thin saturated zones below feedlots located in the “sandy soil areas” where “natural” nitrates are normally higher. The vast majority of the young lots are concentrated in the central and north plains (outside sandy soil zones) where saturated thickness is large (k200 feet).

Normally one finds a higher concentration of nitrate in areas with a shallow depth to water. However, there are notable exceptions to this; for example, Tierra Blanca Draw that extends through Hereford, Texas. Over 100 observation wells around feedlot complexes have been sampled along the draw, and certainly no significant nitrate problem exists in these locations. Perhaps the explanation for this is in part due to stream effluency along Tierra Blanca Draw.

A summary of the relation of feedlot runoff seepage factors to groundwater quality in the Texas High Plains is enumerated in Table 1.


TABLE 1. Relation of Feedlot-Runoff Seepage Factors to Groundwater Quality, Texas High Plains

F a c t o r s Remarks

G e o g r a p h i c l o c a t i o n

Age o f l o t

S i g n i f i c a n t ; r e l a t e d t o s o i l s d i s t r i b u t i o n , geomorphic and g e o l o g i c c o n t r o l .

S i g n i f i c a n c e i n t e r d e p e n d e n t on o t h e r f a c t o r s . Old f e e d l o t s do n o t mean p o l l u t i o n .

F e e d l o t c a t t l e l o a d Not c o n s i d e r e d s i g n i f i c a n t f o r commerc ia l f e e d l o t s .

Feedpen s u r f a c c S u r f i c i a l m a t e r i a l o f f e e d p e n s i s slow t o p o o r l y p e r m e a b l e due t o compact ion and c e m e n t a t i o n .

Feedpen g r a d i e n t Not d i r e c t l y r e l a t e d t o g r o u n d - w a t e r q u a l i t y .

S t r e a m g r a d i e n t Y o r e l a t i o n t o g r o u n d - w a t e r q u a l i t y .

Feedpen a r e a - vs D r a i n a g e - b a s i n a r e a

Type o f c o l l e c t i o n s y s t e m

R a r e l y s i g n i f i c a n t ; o n l y , r J i t h v e r y l a r g e r a t i o s i n s t r e a m s and s m a l l r a t i o s i n p l a y a s .

S i g n i f i c a n t ; p l a y a and non-ponding s y s t e m away from s t r e a m most d e s i r a b l e .

C a p a c i t y o f s y s t e m % D r a i n a g e a r e a Not a lways s i g n i f i c a n t . Depends on l o c a l geology.

C o l l e c t i o n - 5 y s t e i n s u r f i c i a l m a t e r i a l I m p o r t a n t ; p l a y a c l a y impermeable .

S u b s u r f a c e l i t h o l o g y bliniinum p e r m e a b i l i t y s i g n i f i c a n t i n O g a l l a l a .

C a l i c h e “ c a p r o c k “ S i g n i f i c a n c e i s q u e s t i o n a b l e due t o u n p r e d i c t a b l e permeab i 1 i t y .

Uepth t o w a t e r S i g n i f i c a n t i n some g e o g r a p h i c l o c a t i o n s .

S a t u r a t e d t h i c k n e s s b e n e a t h l o t I m p o r t a n c e d e p e n d e n t i n p a r t on t r a n s m i s s i b i l i t y o f O g a l l a l a F o r m a t i o n .

GROUNDWATER QUALITY BENEATH CATTLE FEEDLOTS

In order to discuss this topic we must first establish what comparative water-quality parameters are indicative of cattle feedlot runoff, and the quality of water in the Ogallala aquifer prior to establishment of cattle feedlots.

To characterize cattle feedlot runoff and High Plains groundwater (Ogallala) in terms of common dissolved solids we refer to Table 2. In this table we compare on a relative basis various chemical-quality criteria of Ogallala groundwater to that of feedlot runoff. Of those chemical parameters shown, the nitrogen family, sodium, potassium, chloride and total dissolved soilds (TDS) are the most definitive of feedlot runoff.

There are areas in the southern High Plains, particularly in sandy soil zones, where naturally occurring N03-N in groundwater is higher than in feedlot runoff. Also, there are localities where naturally occurring NO, -N is higher in “normal” Ogallala groundwater than in water beneath feedlots known to be “seeping” to the watertable. The problem then in determining if NO,-N in groundwater is derived from feedlots cannot be evaluated for specific locations unless the “background” or “natural” concentration of NO, -N is known.

Chloride, sodium, potassium, nitrite-N, ammonia-N, organic-N, total-N, and TDS are more concentrated in runoff than in “natural” Ogallala groundwater. However, as with NO, -N, other forms of nitrogen and particularly chloride, sodium, potassium and TDS should be evaluated on the basis of “normal” concentrations in the vicinity of the feedlot in question. Feedlot runoff usually contains from less than one-hundred to several hundred PPM of total nitrogen, chloride, sodium, potassium, and up to several thousand PPM of TDS.

Ionic-concentrations in feedlot runoff are difficult to correlate with concentrations in


TABLE 2. Wzter Quality Parameters: Relative Comparison of OgaUala Groundwater to Cattle Feedlot Runoff

Water Quality Feedlot Ground Water,South Ground Water, Parameters Runoff High Plains North High Plains.

N03-N L L-H L-N

NO2 -N H L L

NH 3 H L L

Total -N H L L

Na H L L

K H L L

Ca N-H L-N L

.Mg N L-N L-N

c1 H L L

s04 L-N L-N-H L-N

TDS H L L

PH L-N N-II N-H

H=high concentration L = 1 ow conc en t r at ion N=about same i n each type of wate r

groundwater of specific ions derived from feedlot runoff. This is particularly true for potassium. It is rare to see correlation of potassium concentrations between infiltrafed runoff and groundwater. Of course, this is in part accountable by plant use of potassium, adsorption by clay minerals, and use of potassium by organisms.

Secondary precipitation of dissolved solids is readily noticeable in the few feet of near- surface material of feedlots and in parts of the unsaturated zone of the Ogallda Formation. This is another cause of the often observed ionic imbalance between cattle feedlot runoff and groundwater.

In regard to the significance of NO,-N below High Plains cattle feedlots, consideration is given to the quantitative distribution of NO3 -N in groundwater in light of the socioeconomic use of groundwater in the region. In this study, NO3 -N values exceeding 10 PPM are arbitrarily selected as the level at which groundwater is considered to be degraded in quality. (Qualitative parameters other than NO3 -N were evaluated but are not presented in this report.) In terms of socioeconomic use of water in the High Plains it is estimated (by others) that less than 5% of the total water consumption from the Texas High Plains Ogallala aquifer is for municipal- household use. Certainly much less than one percent of the total available water from the Ogallala for rural household use exists below cattle feedlots. Groundwater in the High Plains is produced primarily for irrigation and other agricultural practices. Considering the use of groundwater, the low tolerance used in this report for evaluating groundwater quality beneath High Plains cattle feedlots is very conservative.


There are feedlots in the northern and southern High Plains beneath which N 0 3 - N levels exceed 10 PPM. These feedlots range from 4 years to more than 20 years in age. Of the 80 lots reported in this study nine exceed the above-specified arbitrary standard. Of the nine lots, four are due to seepage down open bore holes and two feedlots share the origin for NO,-N with other nearby sources (fertilizers and city runoff). In addition to the aforementioned nine feedlots, perhaps 10-1 5 more feedlots show NO, -N concentration in groundwater higher than the “normal” concentrations in the vicinity of the feedlot.

Figure 5 illustrates the range in maximum NO3 -N concentration in groundwater compared to age of cattle feedlots in this study. The values used to derive the graph represent maximum values in water beneath each lot. Each feedlot used represents 5 to 25 groundwater analyses and the high and low maxima for each year represent 5 to 70 determinations of NO,-N. The dashed line shows the base level for NO,-N beneath feedlots. This base-level has not been corrected for “normal” back-ground levels in the Ogallala before establishment of the feedlot, therefore the base level for feedlot N 0 3 - N contribution is less than shown. The base-line shows a general increasing trend in NO,-N concentration with age. This is a very flat trend and certainly IS not alarming. This same profile, unrelated to feedlots, exists in a north-to-south direction on the Texas High Plains, and probably is related to time and agricultural practices.

11 950 1955 1960 1965 1970

AGE OF FEEDLOTS

Fig. 5. Age of feedlots investigated vs range in maximum NO,-N concentxation in groundwater.

The upper (solid) line of Figure 5 represents the highest maximum level of NO,-N found in all lots. As with the base-line it has not been corrected for “normal” background NO,-N. The upper line tends toward considerable variation in age concentration relationships and indicates, regardless of age, some lots contribute NO, -N to the groundwater zone of the High Plains.

In conclusion, aside from all qualitative ramifications, quantitatively how significant is NO,-N accumulation in Texas High Plains groundwater due to infiltration of cattle feedlot runoff? We will not attempt to document our work and others on the geometry of N03-N distribution in the saturated zone of the Ogallala aquifer but suffice to say that concentrates of chemically mobile dissolved solids in (Ogallala) groundwater rapidly lose identity away from the point source. High N03-N concentrations in groundwater related to feedlot runoff is


only of geographically localized concern in specific areas and, in my opinion, is not and will not in the foreseeable future be a regional aquifer problem.

Percentagewise, the total volume of water now degraded is insignificant, and the total volume of water to be “polluted” by all Texas High Plains feedlots is on the order of +1%. Volumetric considerations related to levels of degradation of groundwater have to be taken into account in the Texas High Plains due to over 95% of the annual consumptive use of groundwater being for agricultural and industrial needs. Actual and potential degradation and/or “pollution” of the Ogallala by High Plains cattle feedlots should certainly be treated in perspective and only on a detailed basis.

LITERATURE CITED

Carter, W. T. 1931. The soils of Texas. Texas Agricultural Experiment Station Bull. 431. Lehman, 0. R., B. A. Stewart and C. A. Mathers. 1970. Seepage of feedyard runoff water impounded in

Lotspeich, F. B. and J . R. Coover. 1962. Soil forming factors on the Llano Estacado: parent material, time, playas. Texas A&M Experiment Station MP-944: 1-7.

and topography. Texas Journal Science 14(1).

Documents

SUBSURFACE DISTRIBUTION OF NITRATES BELOW COMMERCIAL CATTLE FEEDLOTS, TEXAS HIGH PLAINS