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distance from seawater and concentrations of organic matter increase, the <br />concentrations of arsenic, chromium, copper, selenium, uranium, and other elements <br />increase within the formations present in the watershed area. <br />Quaternary deposits overly the bedrock over much of the watershed area. These <br />deposits generally consist of unconsolidated clay, silt, sand, gravel, and sometimes <br />cobbles and boulders. <br />Groundwater in the watershed is found in both confined and unconfined (water table ) <br />conditions. The youngest confined aquifer in the area is the Lower Cretaceous <br />Dakota sandstone, which is not exposed in the watershed. The flow in the Dakota <br />sandstone is toward the northeast and the recharge area of the Dakota formation is <br />the outcrop area to the southwest of the watershed. Activities and surficial <br />contamination sources in the watershed generally have little if any effect on water <br />quality in the confined aquifers. <br />Unconfined conditions in the watershed occur primarily in the alluvial and terrace <br />deposits along the Arkansas River and its tributaries. Groundwater flow in the <br />unconfined aquifer is generally toward the river. Recharge to the unconfined aquifer <br />is from precipitation, irrigation, and leakage from canals, ditches, and drains in the <br />watershed. It is this unconfined aquifer that is the most susceptible to contamination <br />from ineffective irrigated systems, septic systems, feed lots, fertilizer, and pesticides. <br />23 <br />