Horticulture ■ pit

Horticulture Pit. The horticulture pit was constructed in 1969-70 and has been in continuous use since that time. The 8.8 x 3.4 m concrete pit has an average depth of 1 m and has been filled with alternate 30 cm layers of gravel and soil as shown in Figure 1. The soil is a silt loam (Clarion-Nicolett-Webster) characteristic of Central Iowa. A cover closes automatically to prevent precipitation from entering. A tile system constructed below the concrete floor of the pit connects to a sump for sampling of the ground water. The 30,000 L pit has had over 30 kg of more than 40 different pesticides deposited since beginning operation. 

Horticulture Pit. Core samples of soil of about 100 g size to a depth of 10 cm and liquid samples of 500 mL were taken from eight sampling points spaced uniformly across the pit surface. Each sample was then solvent extracted individually and the pesticides and degradation products were separated and quantitated. 

Soil Samples. Five methods of extraction were evaluated for soil samples collected at the Horticulture pit. The results for this evaluation are tabulated in Table II. The Woolson procedure ( 3) was selected for use throughout the course of our investigations of all soil and sediment samples. 

Table II. Comparison of Various Solvents and Extraction Procedures for Recovery of Pesticides from a Horticulture Pit Sample...

Table IV. Pesticide Concentrations October 1977 at the Eight Sampling Points in the Horticulture Pit - y c 2 > 2 D 2 n X >...

Table VI. Disposal Accumulations at the Horticulture Pit in Grams of Active Ingredient (AI)...

Extracts of samples from the Horticulture pit were also analyzed for alachlor, carbaryl, glyphosate, dicofol, MCPP, paraquat, penoxalin and 2,4,5-T. They were either not detected or, if detected, concentrations were <1 ppm. No plots of these results are included in this report. In addition, plots are not included for several pesticides where only results from 1979 were available. These pesticides, with their average ppm concentrations in parentheses, were 2,4-D (40), dicamba (3), metribuzin (25), naptalam (60) and tetrachloroterephthalic acid (30). 

Surrounding Water Analyses. Water samples were taken from a tile system immediately surrounding the Horticulture pit and from sites remote from the location of the disposal pit. These water samples were analyzed to ascertain pesticide leakage from the pit and contamination of the surrounding ground water over that which... 

Figure 3. Plots of the pesticide concentrations in samples of soil (o) and water (X) taken from the Horticulture pit during 1977-1979.

Table VII. Pesticides in Water Samples Near the Horticulture Pit...

Surrounding Air Analyses. The results of the analyses of the air taken above the Horticulture pit are given in Table VIII for the spring and fall of 1979. Air samples were also taken upwind from the disposal pit and most pesticides were not detected or if detected were at their detection limit of K).l ng/L. Volatilization from the pit may be assumed whenever there is an appreciable increase in pesticide concentration in air over the pit relative to an upwind sample taken at the same time. 

Surroundings Summary - Horticulture. From interpretation of the above results for water and air surrounding the Horticulture pit, very little contamination can be attributed to the operation of this pit disposal system. 

The Agronomy pit is also an uncontrolled disposal system so the analytical data are perturbed by the same variables of amount, timing, degradation and losses as described in the discussion of the Horticulture pit. 

As with the Horticulture pit data, the connection of these data points with straight lines is not a valid representation of degradation because of the uncontrolled manner in which the pesticides are deposited. The plots do however give a quick visual representation of possible build-up of any pesticide. Probable degradations may be estimated by comparing the deposition information in Table IX with the analytical data in Figure 4. 

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