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nr 1 y particularly adhere to instructions Provided ure to aeric Oxygen,hence the preferred use of a downhole meter 1t Is necessary to strictly of oxygen to diffuse across a with a given model of Instrument of the membrane to prevent aorOus me DO I DO meters function by permitting a small quantity dep Consequently, it is necessary to keep manually, by a gentle raising and lowertn immediately adjacent to the A water moving in the vicinity maintained g of the meter in the well The rnembraneets delicate and must be rane This can be achieved A negative correlation carefully concentrations should exceed I to occur between DO concentrations and hydrocarbon concentrations atmosphere at the recharge �- for effective aerobic degradation DO In o atmospheric air will contain between or the vadose zone groundwater is dereBackground from the Surface water saturated with oxygen by contact with may vary somewhat de approximately 7 s ,nom at 5°C and 12 75 than those for surface water db g on other chemical parameters DO concentrations g oundwatt though these figures with the groundwater y an amount dependent on the grbndwater DO concentrations Ithe n shallow ngth Of gime the quantity of oxidizable materials a are generally less groundwater has been stored in the aqw fer sulfides) Background ackcontact nd mom- In cool conditions (Hera, 1985 quifers can be as high Aerobic degradation t ) DO may g as I2 mg/I in warm conditions gor as lover as l typically occurs when Eh is approximately+800 mV d groundwater recharge Anaerobic Electron Acca tors (discussed below} (e g Irrigation) Analysis of water samples for nitrate, dissolved bioremediation The higher the background concentratioIr0nns end/or sulfate can insic the Microbes or exceed water provide data atter, unless They are so high as toccreate ative of toxicity for see below}in areas of high quality standards Depleted dissolved electron acceptor concentrations g hydrocarbon concentration are indicative of microbial degradation Narrate Nitrate Of (except iron, laboratory method calculates total nitrate, sincen nitrite Is metastable t quantities to affect the ionic balance Y analyzing nitrate plus nitrite as N human contamination e {Wledemeier et al, 1995 n groundwater and se dom preMethp nt n3 2) This sufficient activity in the site vicinity, agricultural runoff systems) The bulk of nitrates in indicative of a significant biodegradation capacity ) Background eoncentrationsnrytwidel derived from Y. and would othexwlse be commonly less than 1 mg1L reduction typically occurs when Eh is approximately p Y might be those In excess of 20 Y with human +750 rrtV(but more than 0 C°neenirations considered iron ) mom- Denitrification/nitrate Laboratory analysis of iron concentration may sample to obtain the total iron content (precipitated and dissolved) filter Immediately after collection to obtain the dissolved accomplished by collecting an unfiltered groundwater primarily from sail ron , or 6y passing the sample through minerals Dissolved Iron concentratlons care Co ncentration w a 0 4S micron dissolved ferric Iron can oNy exist stably Iron to reduction to ferrous iron occurs at in under values finder groundwater Is derived y under extremely acidic conditions ones a to changes in dissolved iron Is t (pH<2) {Ilam, pH and Eh Free 2995 typically present as a h aerobic, moderate] 1985) Ferric Iron Dissolved ferric Iron is usually rapidly reprecipitated as a sulfide o hydroxide, the ferric species is ferric orthohydroxlde (Wtedeineler et insoluble sedimentary ferric ironoxides Y acidic or alkaline conditions, fatal dissolved iron is indicative of and s as h it energy oxide or hydroxide al, gy source, ProducingSince microbes utilize Ydrocarbon degradation more soluble ferrous: iron, an increase in The solubility of ferrous iron is significantly reduced b {Barker et al, 1995 Y the presence of sulfides,the end-product of sulfate Analytical results of dissolved ferrous Iron concentration will like since it is not based on the actual amount of fe rric amount of reduced ferrous iron (the end product)remaining In solution at the a reduction hydroxide {the electron acceptor) cce for likely give an underestimate, Typical background concentrations of total dissolve p } present in the aquifer, but the time of sampling 1 0 Mg/`L indicate It conditions (Cookson, High dissolved iron concentrations may iron 5 groundwater are below l p n, degradation 1995 1/. Results In excess of high organic content High organic content induces stability} which may have resulted from anaerobic hydrocarbon of the y also indicate the presence of very fine particulates low total iron content of a sample is useful as a background datum a dissolved concentration of soluble iron complexes (Fle,n 1985 pH, or arily frorn soil gainst which to compare Chanes r nm he r Sulfate Sulfate is derived the presence of black acid volatile sulfide deposits minerals he occurrence rr nce Of sulfate reduction may be inferred from long-term contact with contaminated groundwater CLEARWATER GROUP(NATURAL ATTENUATION) 4 revised October 3,2002