An Introduction to Groundwater Groundwater Topics The occurrence

An Introduction to Groundwater

Groundwater Topics The occurrence of groundwater. n Well construction. n Useful data to collect. n Groundwater / Drinking water protection. n DHS Drinking Water Program

Groundwater Basics n n Where does ground-water come from? How does ground-water occur? How does ground-water move, what direction and how fast does it travel? How susceptible is groundwater to contamination? DHS Drinking Water Program

Important Groundwater Facts èGroundwater originates from precipitation sinking into the ground from the surface to the water table. è Groundwater occurs in the open spaces between silt, sand gravel particles or in natural fractures in rocks (not underground rivers or lakes). è Groundwater moves from where the water table is high to where it is low. è How fast it moves depends on aquifer permeability. è Groundwater is susceptible to contamination from surface activities. DHS Drinking Water Program

Origin of Groundwater DHS Drinking Water Program

Aquifers Once water reaches the saturated zone it is called groundwater. n If the geologic material of this saturated zone is permeable and can yield water to a well in sufficient quantity to supply user needs, it is referred to as an aquifer. n Aquifers can be either unconfined or confined. n DHS Drinking Water Program

Occurrence of Groundwater DHS Drinking Water Program

Types of Aquifers n Unconfined – – n Shallow Local Recharge Water Table Susceptible Confined – – – Deeper Confining Layer Distant Recharge Water under pressure Less susceptible DHS Drinking Water Program

Local vs. Distant Recharge DHS Drinking Water Program

Alluvial Aquifer: Valley Fill Stream Bedrock High yield High/Local recharge rate DHS Drinking Water Program Alluvium Bedrock

Bedrock Aquifers n Fractured bedrock – – n Water in cracks Low/High yield Low/High recharge rate “Dry” holes Layered volcanics – Water between flows – High yield – Low recharge rate DHS Drinking Water Program

Groundwater Flow A common misconception – groundwater does not flow in underground rivers. n Instead, groundwater exists within the saturated zone in pore (open) spaces and travels by seepage (percolation). n How easily water travels underground is a function of the type of sediment present. n Permeability: gravel > sand > clay n DHS Drinking Water Program

Groundwater Movement DHS Drinking Water Program

Groundwater Levels Groundwater levels fluctuate over the course of the year, especially in shallow aquifers. n Generally, groundwater levels rise during the high rainfall, winter months and fall during the drier summer months. n Additionally, the higher level of pumping of wells in the summer impacts groundwater levels of wells through drawdown. n DHS Drinking Water Program

Seasonal Water Levels: Winter DHS Drinking Water Program

Seasonal Water Levels: Summer DHS Drinking Water Program

Groundwater Composition: Variability Between Wells • Recharge and/or source related • Wells screened in different aquifers • Wells screened at different depths in the same aquifer DHS Drinking Water Program

Seasonal Compositional Variations n n Seasonal Differences within a single well Recharge related – Infiltration of nitrate from a nitrate source (A) – Dilution of contaminated aquifer (B) n Significant Variations – Up to 100% have been observed, e. g. , <10 to >20 mg/L DHS Drinking Water Program A B

Useful Data to Collect n n n Down hole video log (at construction). Spinner log (at construction). Static water-levels (minimum of spring and fall). Aquifer test to calculate specific capacity of well (gpm/drawdown – annually). Monthly water use. Major ion chemistry. – Sodium, Calcium, Potassium, Magnesium. – Sulfate, Chloride, Bicarbonate, Carbonate. DHS Drinking Water Program

What is a Source Water Assessment? n Delineation – Groundwater: Identification of the land area above the well or spring’s capture zone (DHS) – Surface Water: Identification of the subwatershed area above intake (DEQ) n n n Inventory of Potential Contaminant Sources Determination of the susceptibility of the drinking water source to the PCSs Written Source Water Assessment Report DHS Drinking Water Program

GPS Well Site n n Necessary to have gps coordinates in latitude longitude Correct Well location on map relative to the drinking water protection area (DWPA) DHS Drinking Water Program DWPA Well

What is the Datum? n n In order for the well location to properly register on the map, latitude/longitude location of well must be relative to the same datum as the map. Record as NAD 1927 or WGS 1984 DHS Drinking Water Program

Procedures for Delineation: Groundwater Identify that part of the aquifer that supplies water to the well or spring n Site-specific parameters n Radius a function of time n Project to the surface n DHS Drinking Water Program

Drinking Water Protection Areas: Oakhill School DHS Drinking Water Program

Multiple Well Delineation DHS Drinking Water Program

Drinking Water Protection Areas: Junction City DHS Drinking Water Program

Hydrogeologic Mapping DHS Drinking Water Program

“Potential contaminant source” n n n a location where there is any activity having the potential to release one or more contaminants into water at a concentration of concern Database queries (14), field locating in sensitive areas, PWS consultations 96 separate categories of PCSs As of 7/05, over 15, 300 PCS locations have been identified focus must be on HIGHER risks DHS Drinking Water Program

Drinking Water Protection Process for Public Water Systems (PWS) GPS intake or well and request PWS assistance DELINEATION of the source area or “Drinking Water Protection Area” Activate community citizens, gather input, select a few strategies for protecting the source area INVENTORY for “Potential Sources of Contamination” per guidance OPTIONAL: Consider writing a Drinking Water Protection Plan and gaining certification from DEQ Determine SUSCEPTIBILITY to contamination SOURCE WATER ASSESSMENT REPORT Sent to PWS DHS Drinking Water Program IMPLEMENT the strategies to prevent contamination Drinking Water PROTECTION phase Source Water ASSESSMENT phase DHS and DEQ contact PWS;

Source of Information Source Water Assessments: 1996 Amendments to Safe Drinking Water Act n Purpose of SWAs: To provide information water systems need to protect their resource n – Identification of drinking water source area – Inventory of potential contaminant sources – Determination of the susceptibility of the drinking water to those PCSs n Most Oregon PWSs have received reports DHS Drinking Water Program

DHS Drinking Water Program

DHS Drinking Water Program

Oregon drinking water source areas for surface water intakes DHS Drinking Water Program

Oregon Drinking Water Protection Areas from Groundwater Sources DHS Drinking Water Program

Planning for Growth DHS Drinking Water Program

Planning for Growth DHS Drinking Water Program

DHS Drinking Water Program

Developing Protection Strategies n Use Source Water Assessment to identify highand moderate- risks. Update list – – n Evaluate based on – – n Risk factors Aquifer sensitivity Benefit achieved (risk reduction, economic factors) Challenges (time, staff, cost) Community buy in Long-term plans Associate appropriate BMPs with each identified risk DHS Drinking Water Program

Implementation Matrix: Prioritizing the Approach Benefit Time Line < 6 months Lower High Risk Site BMP Easy to do 6 months – 2 years > 2 years Moderate Low Risk Site BMP Hard to do DHS Drinking Water Program

DHS Drinking Water Program

Summary n n Source Water Assessment Reports help identify potential threats to drinking water quality. The goal of Drinking Water Protection is to reduce the risk of contamination, not necessarily eliminate it DEQ/DHS can assist public water systems prioritize their protection efforts and identify specific strategies Drinking Water Protection in Oregon is voluntary but is necessary in order to protect existing and future drinking water sources. DHS Drinking Water Program