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Houston Engineering 103rd Street Storm WaterZ/1 I DRAFT J HnNQ) Date: October 27, 2006 To: Matt Moore 1 Executive Summary Houston EngMeering, Inc. 10900 73` Ave. N., Ste. 106 Ph. (763) 493 -4522 Maple Grove, MN 55369 Fax (763) 493 -5572 From: Wesley Saunders- Pearce, Brennon Schaefer Subject: 103 Street Stormwater Quality Analysis The objective of this project was to generally characterize a level of concern regarding potential groundwater impacts due to the infiltration system being constructed in/near bedrock material. The results of this modeling study show that the level of concern attributed to this project is high. This conclusion was due to the fact that the changes in nutrient and sediment loadings (nitrate, chloride, and total suspended solids) are statistically significant and that the 103` Street site is located within an area that is poorly suited for large -scale infiltration. Recommendations include ensuring a spill plan is in place, incorporating additional site design elements, and considering detailed modeling analysis for further risk characterization. 2 Project Overview An infiltration basin is being constructed in Cottage Grove. The basin is intended to provide water quantity control benefits due to historic flooding along 103r Street, as well as a planned expansion of a facility adjacent to this area. The infiltration basin was designed to be approximately 40 feet deep with a capacity to fully store runoff from up to a 100 -year rainfall event over an area that is approximately 118 acres in size. The construction involves enlarging the existing natural depression along the west edge of the property and diverting more runoff from the property to this basin. The infiltration basin will have a bottom elevation at 708 feet mean sea level (MSL), placing it at bedrock conditions. No water quality analysis was performed prior to construction. The objective of this project was to generally characterize a level of concern regarding potential groundwater impacts due to the infiltration system being constructed in/near bedrock material. 3 Approach 3.1 Model To meet the objective of this project, a straightforward mass - balance oriented spreadsheet model was adapted to generally characterize water quality dynamics at the 103r Street site. The model of choice was the PondNet model. The original model structure was altered to simulate flow and nitrate (NO3), chloride (Cl), and total suspended solids (TSS) parameters. These constituents were selected as indicators for groundwater impacts. The PondNet model for this project was linked with the Crystal Ball program to add a stochastic nature to the modeling scenarios, thus allowing a level of uncertainty in the project analysis to be considered. Using Crystal Ball, a range of nutrient concentrations and environmental conditions were simulated and examined. Multiple simulations were also run simultaneously with Crystal Ball. This resulted in a number of likely outcomes, • Page 1 of 6 0 which increased the predictive strength of the PondNet model. Descriptive statistics of mean, median, 95 percentile confidence interval about the mean and median, and the lower and upper quartile range (25` and 75`" quartile) about the median were calculated, and box plots were produced to visually display the statistics produced for the output. 3.2 Inputs There were a variety of input variables necessary to construct the PondNet model. These were a record of rainfall, as well as land use, drainage area contributing to the infiltration basin, and an estimation of the nutrient concentration for the different land use practices. A historical record of annual rainfall depths, ranging from 1933 -2005, was used as the basis for the rainfall input. Precipitation data used for this project was from the Hastings Dam site (station 213564), located in Hastings, MN. It was found that a beta distribution described the characteristic of the rainfall data, and this distribution was used as the precipitation input component to the model. Land use was based upon a Barr Engineering study that was performed for the 103` Street site to investigate stormwater improvements using the XP -SWMM model. Two general, simplified land uses were gleaned from this study, which were nursery "fields" and "green house ". These land uses were verified by site reconnaissance, as noted in Figure 1. Once these land uses were set, the annual runoff coefficient (Rv) could be estimated for them. The Rv value simply reflects the proportion of total annual precipitation that occurs as runoff volume. This coefficient is a direct function of land cover and use. The range of Rv values used in this study for the two land uses can be found in Table 1. Contributing drainage areas for the pre and post construction periods were also based upon the Barr Engineering study. The overall watershed boundary, pre and post infiltration pond contours, and storm system improvement characteristics were used to estimate the drainage boundaries. The contributing drainage areas were digitized with Geographic Information Systems (GIS) software (Figure 2). The pre - project contributing drainage area was determined to be mostly fields and was calculated to be 45 acres in size. The post - project contributing drainage area was determined to be a mix of fields and green house area. The post - project area was calculated to be 118 acres in size, of which 102 acres was generally fields and 16 acres was green house area. The parameters of interest in this study were NO3, Cl, and TSS, as stated earlier. Nutrient concentrations for the different land use practices can be found in Table 1. All of the input data used in this study, except rainfall, was defined as having a uniform distribution. The uniform distribution allowed uncertainty in the estimations to be accounted for in the calculations, with any of the values in that range being equally likely to occur. 4 Model Results The largest affect that the new stormwater improvement project has on the 103` Street site is the increase in contributing drainage area to the infiltration basin. The new improvements increase the contributing drainage area by about 2.5 times. This has the effect of increasing the runoff volume going to the infiltration basin, which can be observed in the box plot produced for the runoff volume data (Figure 3). The median runoffvolume for the pre- project drainage area was 18 acre-feet per year (ac- fl/yr), while the median runoff volume for the post - project drainage area was 61 ac-ft/yr. This represented a statistically significant change. • Page 2 of 6 IMINM The reason the increase in runoff volume is important is that it has the effect of increasing the nutrient and sediment load being delivered to the basin. This can be observed in the box plots produced for the modeled Cl, NO3, and TSS loads (Figures 4-6, respectively). The median Cl, NO3, and TSS loads being contributed from the pre- project drainage area was calculated to be 4,135,184, and 6,739 pounds per year (lb /yr), respectively; the median Cl, NO3, and TSS loads being contributed from the post- project drainage area was calculated to be 10,798, 484, and 19,266 lb /yr, respectively. Most of this increase in load is due to the increased contributing area coming from what was defined as fields in the modeling study. Of the additional 73 acres being contributed to the infiltration basin following post- project completion, 57 acres is from fields. Concentrations of the parameters were then calculated in the basin on a pre- and post-project basis. Potential concentrations in the basin were calculated on a yearly basis by dividing the total runoff load by the total basin runoff volume. The calculated concentration ranges for pre - project Cl, NO3, and TSS can be found in Table 2, while the ranges for post - project Cl, NO3, and TSS can be found in Table 3. It should be noted that these calculated concentrations are only volume weighted estimates and represent a coarse- scale, annual estimate. These are conceptual estimates reflecting theoretical, fully mixed conditions in order to approximate a potential level of concern. Field data collection performed by others at and around the 103 Street property was used to verify the model output. The only constituent available for comparison in both studies was nitrate nitrogen. The first set of data was from field sampling that was performed at the 103 Street property. The only data used from this study was collected from the infiltration basin of interest for 2005. This data can be found in Table 4. The second set of data was from a Cottage Grove area nitrate study performed by Barr Engineering in 2003. This data was collected from a series of groundwater monitoring locations. Four locations from this study, near to the 103 Street property, were used (Figure 7). This data can be found in Table 5. It was found that the modeled NO3 concentrations were within the range of values found in the two studies on a pre and post project basis, albeit on the low end of these ranges due to the conservative nature of this study. Discussion of Findings A variety of tools were used to evaluate a potential level of concern for the stormwater improvement project. These tools ranged from comparing modeling results with state water quality standards, assessing relative changes in nutrients and sediment being delivered to the infiltration system, applying maps and information on the groundwater system for the area to determine infiltration suitability, and reviewing guidance documents on infiltration basin siting. 5.1 Standards Comparison The calculated water quality parameter concentrations from the trial runs were compared with Minnesota state standards. The Minnesota Department of Health (MDH) health risk limit for drinking water standards of 10 mg/L was used for NO3, and the Minnesota Pollution Control Agency (MPCA) class 2B waters standards of 230 mg/L was used for Cl. It was found from this comparison that none ofthe modeled NO3 and Cl annual runoff concentrations exceeded the comparison standards. This was expected and due to the fact that the input concentration ranges for NO3 and Cl were conservatively based (i.e., low). These findings should not be taken literally, however, as the calculated values were coarse - scale, annual estimates. If the modeling study was performed on a finer scale, such as daily, variations in nutrient and sediment concentrations could have been more precise. • Page 3 of 6 K 1 5.2 Relative Changes in Nutrients and Sediment It was found that the changes in nutrient and sediment loading found in Figures 4-6 are statistically significant, based on the values used for input to the model. Even though the specific loadings to the basin are estimated from assumptions made with the initial nutrient and sediment concentrations, it is known that then drainage area contributing to the infiltration basin will increase with the improvements made to the stormwater system at the 103' Street site. The increase in contributing drainage area will increase the volume of runoff being delivered to the basin, and thus the total mass of nutrients and sediment being delivered to the basin will increase. 5.3 Infiltration Suitability The study area was compared against the regional infiltration suitability map developed for the South Washington Watershed District Draft Watershed Management Plan (Figure 8), which is considered a screening tool for infiltration basin siting. Regional infiltration facilities generally tend to concentrate runoff into one location and as such do not truly mimic the natural predevelopment hydrology of a project area. Regional infiltration basins typically serve primarily to provide flood control benefits and mitigate downstream water level issues. The concentrated volume of water diverted to centrally located regional infiltration basins may increase the risk for groundwater impact. The screening tool balances the physical capacity to incorporate infiltration against how quickly infiltrated water may reach deep groundwater sources (Prairie du Chien -Jordan aquifer). The Prairie du Chien -Jordan aquifer area in South Washington County is typified by karst geology, which refers to a type of topography that is formed over limestone by solution of the rock and is characterized by closed depressions or sinkholes, caves, and underground drainage. From review of the screening tool, it was found that the 103' Street site is located within an area that is poorly suited for large -scale infiltration. It is also located near known karst features (springs and sinkholes). 5.4 Guidance Document Review Various documents were consulted for guidance on siting of infiltration basins. The Minnesota Stormwater Manual section "Additional Guidance for Karst, Shallow Bedrock, Groundwater, Soils with Low Infiltration Capacity, PSHs, and Sediment Disposal Areas" was a main guide. It was found that the Minnesota Stormwater Manual recommends that if stormwater cannot be removed from an area with karst geology, the water should undergo extensive pretreatment and the pond should be engineered with a synthetic liner. A minimum of three feet, and preferably ten feet, of unconsolidated soil material should exist between the bottom of the pond and the surface of the bedrock layer. It was also recommended in the Manual that a water quality monitoring system should be installed to keep track of potential groundwater impacts. The MDH Appendix A "A Flow Chart for Evaluating Proposed Stormwater Infiltration Projects in Areas with Vulnerable Groundwater" and the Center for Watershed Protection's Stormwater Center Screening Matrices also discourage infiltration basin siting in areas of karst. Summary and Recommendations In summary, this study was performed to provide a general characterization of the level of concern that should be raised with regards to potential groundwater impacts from the infiltration system constructed in/near the bedrock material located at the 103` Street site. From review of the report given by Barr Engineering on the 103' Street property proposed stormwater management improvements, the review of the Minnesota Stormwater Manual, and the results of this modeling study, it is believed that the level of concern attributed to this project is high. • Page 4 of 6 14 This level of concern is qualitatively assigned due to: • Pretreatment ofthe runoff water was not incorporated into the infiltration system upgrade and design plans. • There were no considerations to allow adequate separation between the bottom ofthe basin and the bedrock surface, such as including a liner or soil barrier at the bottom ofthe infiltration basin. • A geologic investigation should have been performed prior to the start ofthe construction ofthe infiltration basin to characterize the nature ofthe karst found at the site. • The modeling results from this study show that there would be statistically significant differences between pre and post project loadings to the infiltration basin. The findings from the modeling study were noteworthy for the fact that an increase in TSS loading to the basin would increase sedimentation, suggesting potential failure (clogging) ofthe infiltration system. Also, NO3 and Cl pose drinking water hazards. The Prairie du Chien Group is the first bedrock unit encountered in the area, and depth to bedrock is locally very shallow. The Prairie du Chien Group is hydrologically connected to the Jordan Sandstone and these units are typically treated as a single aquifer system. Geologic studies in the area of South Washington show that the groundwater flow path for this aquifer is generally to the southwest of the 103` Street site. The Mississippi River is down gradient ofthe site, where groundwater is known to discharge. This has larger regional implications as NO3 delivered by the Mississippi contributes to the hypoxic zone in the Gulf of Mexico. Based on the findings of this modeling study and report, the following recommendations are made. A spill control plan should be developed for the 103` Street site, if there is not one currently. This study only investigated the impacts of nutrients and sediment because these are surrogates to estimate groundwater impacts. Based upon land use at the site, there is also the potential for impact to groundwater due to other contaminants of concern, such as fertilizers and pesticides. Depending on site activities, some businesses are legally required to develop and maintain a spill control plan, formally known as an incident response plan. The plan should generally contain/identify where chemicals are stored, where these chemicals would drain in the event of a spill, and list what to do in the event of a spill (including a phone contact list). The MDA and other state agencies are resources for guidelines or templates on pollution prevention and spill control measures. Details can be found at bq: / /www.mda. state. mn. us/ incidentresponse /responseplan.htm The Minnesota Department of Agriculture (MDA) has authority provided under the Minnesota Groundwater Protection Act to be the lead agency in managing agricultural chemical contamination. The MDA administers Minnesota rules which, among other items, address storage and pollution prevention requirements. The incorporation of additional design elements to address water quality should be strongly pursued. Based upon communication between the land owner and the City of Cottage Grove, it appears that the infiltration basin construction project is ongoing and slated to be completed in approximately five years. This fact facilitates incorporating improvements into the infiltration basin system design. If construction of the infiltration basin is to continue, Minnesota Stormwater Manual guidelines should be followed. Specifically, a more prudent and responsible long -term design for the infiltration basin would include the following elements: The runoffwater being discharged to the basin system should go through a pretreatment process, such as a vegetated buffer. Studies show vegetated buffers can reduce nitrate and sediment concentrations in runoff discharge. The basin design should be reformulated to decrease the excavation depth and spread the basin over a wider area, allowing for a soil barrier between the stormwater and bedrock. At minimum, soil • Page 5 of 6 0 7M m material should be incorporated as a basin "liner" to provide more appropriate separation from the bedrock in order to trap or treat pollutants before they reach the groundwater or bedrock. Establish water quality monitoring well locations to sample groundwater chemistry for indicators of potential impacts. The operators ofthe 103' Street site routinely take on -site grab samples of surface water quality. Groundwater sampling by the operators could integrate successfully to this effort General attention to other industry standard approaches for suitable infiltration basin application and design as discussed in reference manuals such as the Minnesota Stormwater Manual, the Metropolitan Council Urban Small Sites BMP Manual, and more. An expanded water quality analysis based on this study should be considered to investigate the differences between annual loadings to the basin versus event -based loadings and concentrations. The expanded model could also be used to investigate groundwater mixing dynamics. Several figures included in the South Washington ground water study (Integrating Groundwater & Surface Water Management Southern Washington County, 2005) show groundwater potentiometric elevations. Additionally, Figure 51 in this study generally shows that groundwater moves in a southwesterly direction from 103' Street at a discharge rate of about 14 cubic feet per second towards the Mississippi River. An expanded analysis would allow for a more precise quantification of the groundwater concern and would include consideration of downstream receptors. • Page 6 of 6 Tables Parameter Distribution Minimum Maximum Source Fields Rv uniform 0.14 0.21 1 Green house Rv --------------------------------------- Parameter uniform - - - - -- Distribution 0.52 ------- - - - - -- Minimum Minimum (mg/L 0.59 -------- - - - - -- Maximum (mg/L 2 2 ____ _ Source Fields NO3 uniform 3.60 4.00 3 Fields CI uniform 75.0 100.0 4 Fields TSS uniform 130.5 145.0 3 Green house NO3 uniform 1.08 1.20 3 Green house CI uniform 22.5 25.0 5 Green house TSS uniform 67.5 75.0 3 Table 1: Estimates made for model assumptions based on land use practices. General Note: Runoff and contaminant transport from nursery fields and green house land uses are not well documented. For this project, it was assumed that that the green house land use is generally similar to a commercial /industrial (C/1) land use. Fields land use was considered generally similar to cultivated land. Sources 1) For fields, the coefficient utilized 28.5" of annual rainfall which is the median value of Hastings Dam historic rainfall data. An annual runoff range of 4 -6" was used to provide the bounds for uncertainty, based on Figure 7 -1 from the SCS Hydrology Guide For Minnesota showing the isopleths of annual runoff depth near Washington County. 2) For green house, approximately 65% impervious was assumed and the runoff coefficient was derived from the Simple Method regression. This imperviousness is nearer to town home density development than commercial / industrial land use. A lower value was chosen but balanced with the assumption that the green house site is fully connected with site drainage system. 3) Adapted from the Rouge River National Wet Weather Demonstration Project study (Cave et al., 1994), simply to keep data about land use and pollutant parameters from the same source as much as possible. 4) Chloride concentration data in fields /nursery runoff is scarce. On -line publications were accessed to provide context for chloride concentrations in raw runoff from nursery fields. Materials indicated that soil concentrations for chloride should not exceed 300 parts per million (mg /L) in order to maintain crop growth. Values in this model reflect 25% - 33% of 300 mg /L as a potential representation of chloride leached from soil during runoff events. 5) Chloride concentration data for green house runoff is scarce. The Center for Watershed Protection (CWP, 1997) indicates the average chloride concentration in urban runoff is 230 mg/L. Values in this model reflect approximately 10% of 230 mg /L as a potential representation for chloride transported from green house surfaces, because there is no foot or vehicle traffic or other interaction associated with this surface. Tables Trial Cl NO3 TSS Trial CI NO3 TSS Trial CI NO3 TSS (Mg/L (Mg/L (Mg/L m /L m /L (mg/L m /L m /L m /L 1 94 4 141 : 35 87 4 125 2 61 2 91 36 60 2 86 69 53 2 88 3 30 1 55 ! 37 68 3 104 ! 70 58 2 86 4 68 3 113 I 38 45 2 72 I 71 37 2 63 5 39 2 70 I 39 56 2 91 I 72 61 3 111 6 36 2 60 40 33 1 55 73 66 3 94 7 36 2 68 41 94 4 130 74 68 3 106 8 75 3 104 : 42 46 2 76 : 75 63 3 100 9 45 2 76 ; 43 78 3 120 76 63 3 96 10 73 4 126 ! 44 49 2 84 ! 77 71 3 120 11 42 2 73 I 45 84 3 121 I 78 39 2 67 12 93 4 142 I 46 63 3 112 1 79 54 2 83 13 81 4 137 47 76 3 105 80 53 2 83 14 61 3 114 48 53 2 79 81 55 2 79 15 41 2 59 49 88 4 138 82 70 3 106 16 89 4 131 50 61 3 108 83 25 1 43 17 82 4 142 51 23 1 41 84 62 3 107 18 50 2 72 ! 52 57 3 92 ! 85 66 3 96 19 101 4 144 1 53 83 3 130 I 86 82 3 131 20 33 2 58 j 54 76 4 121 j 87 64 3 109 21 49 2 77 55 51 2 89 88 48 2 80 22 82 4 143 56 53 2 76 89 57 2 84 23 77 3 127 : 57 75 3 112 90 67 3 94 24 42 2 68 58 57 2 89 91 93 4 136 25 61 3 98 ! 59 76 3 115 ! 92 76 4 128 26 72 3 109 I 60 99 4 144 I 93 71 3 119 27 60 3 101 I 61 75 3 112 I 94 57 3 94 28 58 3 101 62 65 3 118 95 91 4 154 29 57 3 102 63 62 3 99 96 95 4 143 30 62 3 95 : 64 78 3 117 : 97 36 2 63 31 76 3 117 65 47 2 73 98 61 2 82 32 76 3 108 ! 66 60 3 99 ! 99 59 2 82 33 55 2 74 67 68 3 115 100 59 2 86 34 81 1 4 1 141 I 68 84 4 133 I Table 2: Calculated pre - project concentrations as theoretical annual concentrations for the infiltration basin given fully -mixed conditions. Tables Trial CI NO3 TSS Trial Cl NO3 TSS Trial Cl NO3 TSS (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L (mg/L m /L 1 70 3 117 : 35 63 3 101 2 45 2 77 36 45 2 74 69 40 2 74 3 23 1 46 ! 37 52 2 90 ! 70 42 2 70 4 50 2 92 1 38 34 2 59 1 71 29 1 55 5 30 2 59 I 39 42 2 75 I 72 46 2 91 6 26 1 49 40 25 1 46 73 49 2 77 7 28 1 57 41 69 3 109 74 52 2 92 8 57 2 89 42 34 2 62 75 48 2 86 9 35 2 66 43 58 2 98 76 47 2 78 10 56 3 104 ! 44 37 2 70 ! 77 54 3 99 11 33 2 64 1 45 62 3 102 1 78 29 1 54 12 69 3 116 I 46 48 2 91 I 79 41 2 70 13 60 3 112 47 57 2 92 80 39 2 66 14 47 2 97 48 40 2 66 81 41 2 67 15 30 1 49 49 66 3 116 82 54 2 93 16 66 3 106 50 45 2 88 83 19 1 36 17 63 3 120 51 18 1 34 84 46 2 87 18 36 1 58 ! 52 44 2 81 i 85 51 2 83 19 74 3 115 I 53 63 3 107 1 86 62 3 110 20 25 1 49 j 54 57 3 103 j 87 48 2 91 21 38 2 66 55 39 2 73 88 37 2 69 22 63 3 119 56 39 2 63 89 42 2 67 23 58 3 104 : 57 55 2 92 : 90 51 2 80 24 31 1 57 58 44 2 77 [7j T1 70 3 115 25 45 2 78 ! 59 56 2 95 ! 92 57 3 105 26 53 2 88 1 60 72 3 117 1 93 54 2 97 27 1 45 2 83 I 61 55 2 92 I 94 44 2 81 28 44 2 84 62 49 2 95 95 68 3 127 29 43 2 82 63 47 2 85 96 70 3 115 30 47 2 83 : 64 58 2 97 : 97 27 1 51 31 56 2 95 65 35 2 61 98 45 2 68 32 57 2 91 ! 66 44 2 80 ! 99 44 2 71 33 41 2 63 1 67 51 2 93 1 100 44 2 72 34 1 60 3 115 1 68 63 3 1 108 1 Table 3: Calculated post - project concentrations as theoretical annual concentrations for the infiltration basin given fully mixed conditions. Tables Table 4: Sampling results from the 103 St. site property. Note — The Gate Pond is understood to represent the infiltration basin of interest in this study. Site ID Number Gate Gate Gate Gate Site ID Pond Pond Pond Pond Date 7/5/2005 7/12/2005 7/1 9/2005 7/26/2005 _.........._.........__..__... Nitrate - Nitrogen 3.0 .........___._— ___......._— 3.0 4.0 3.0 m /L Gate Gate Gate Gate Site ID Pond Pond Pond Pond Date 8/2/20 8/9/2005 8/16/2005 8/23/2005 Nitrate - Nitrogen 5.0 4.0 4.0 3.0 m /L Table 4: Sampling results from the 103 St. site property. Note — The Gate Pond is understood to represent the infiltration basin of interest in this study. Site ID Number 31 36 41 79 Unique Well ID 481262 577046 121063 179806 Date 11/13/2002 11/19/2002 11/19/2002 11/13/2002 Nitrogen Nitrate m /L 8.2 <0.05 10 20 Table 5: Sampling results from Cottage Grove area nitrate study. See Figure 7 for well locations. Q Pre- project drainage Post - project additional drainage Sources: Watershed boundary- Barr Engineeri ng report Drainage boundaries - Houston Engineering Background - 2005 Wash ngton county aerial photos watershed boundary 0 375 750 1,500 Feet Figure 2 1 1 1 1 1 1 f I i O) N (7 .T T m C a a T N C N O O O N N O U r. I d i+ c M 0) d 6 L6 O O O O O [� LO rn � N � N d M •- O M C 00 r- R — O . d r C CO d O d — O O O V O O \° 1-- 00 � r LO 07 M d L O C V d . L n N O a 0) d H U C C c c w .Q E y O L a ttz O c 3 t 0 Q. 0 C L 0 'O 0) C O ` Q L�J a O 0) 0 n ( LO IT M (N O O jAAI LO LO (D co V: U � O <- W co O LO LO (D M o 'IT LO r N N (D O O N CD 0 := 4- O O C C � 3 L L V V O O L L a a d ) L W O. O Q LL n a� N N m 3 v a� N T m C l0 U C C C S i d 0 n LO O c L( ? I` 13 I- M 'a � U) d L f' r O O M U) N a) co O m O O �y O O v r U r O Q� C to co fC M O O O O LO c � 2 -- 24 - - O O O V L r a c� 0 J d a Q L V V d �O L a 0 a d a ` i+ U G tT c c c w c O z 7 O 2 .Q E O d e O M C I- C) O N LO O � O �- I` LO LU — O 0) — N 4.1 4 v 0 N N O . L L CL m d d+ IZ O Q U U d' d L LL V N �i' 0) 1- 0 o 0 rn CL N N a cqcq AD N W c U7 U7 a) d V O a N ° o ° O _Q °O ° o ° 0 0 ° o ° o ° o ° o ° o ° c N ( d N O 0 ( V jA /ql 4.1 4 v 0 N N O . L L CL m d d+ IZ O Q U U d' d L LL C7 U) T m Q .c 3 T (6 c f0 c C C i 1 C d a+ N c� 0) N N LO O O O r d U 00 N \° N d� (1) 1 00 M O 1� r � O O N N c 00 d' f0 CO o0 :0 r- d N 2 M O = O "': 0) O — Lo O O O V , It o LO ( r d' 07 J G1 L 7 O J d L V d . a N O 0. ui d L IL F- U C c c c W c O O v W E `o Gf a O r O � W � 'o 'o ,b a .r Q N Q- O. M W, • IS U N co M -- - 'o a Q N rn It cli M O z d' ti N N N O LO Cl) W dam' - - 9 -° Q M O O O z o 0 r r c 0 0 0 0 0 0 o 0 0 0 0 0 00 I-- (O N d' M 0 0 0 0 N r- 0 jAlgl 'o 'o ,b a .r Q N Q- O. M W, • IS n f0 O O N .. N N - fl O > U @ O t O r 3 a ro N T ro c d ro +, N a O J N V , O N a m a C d Q. N 7 N R O F- v d . L a N O C. N d L a N a H ) (3 c C a) c W c O O .0 . a) E y O L aD a m --- C, °o C) LO t'i (D . L co 0 CL M H U a) �O N Q. V N � Q. 4= Y) U) 0 (o W N (0 O_ O � N O O M 0) U n � 0) N o LO � M (0 ti I N N O rl-: M 0) co LO d N ti — I LQ M c 0) f0 m M (0 O r d 0 r- = a0 ( O r— N O O U M O � co rn (0 00 L ti CO M W r 0 y r r M N LO I\ OR r O co co LO O r rl� C N �_ d � � 00 0 0 v 4� N N O Q Q. L � Q N n a »N F- w d L n O o Lo ° o M N N jAlgl CGANS sample locations Sources: r, V%tershed boundary - Barr Engineering report MM ac CG ANS sample locations -Barr E ngi need ng LXM NoSfq tD l7vraQ Background - 2005 V%shington county aerial photos 170 0 500 1,000 2,000 Feet Figure 7 UVatershed boundary Nitrate Study Sanufflina Lacatiens WASHINGTON RADLSEY Y SVVM Pdlical Boundary Infildration Suitability s -- Bedrock Fault Location VMershed boundary M Low Karl Features Courtly Boundary JM Marginal ® Sinkhole VW ter Features (MN DNR) Moderate ♦ Spring Vtit3terbody High ® 1,000 Foot Faults a Karst Features Buffer '., Island VMer Stream Qntermittent) ---- - - - - -- Drainage Ditch Date Sources Washington Conservation District, Washington County, Metro GIS, MN DNR Data Deli, MN Geoloj cal Survey, Houston E rgineering, Inc., BARR Engineering. Infiltration suitability grid generated from the combination of an infiltration grid generated from infitration potential point date created by BARR Engineering, and a groundwater senstMtylo pollution grid generated torn the Mshington County Prairie du Chen-Jordan Aquifer Senstivityto Pollution data. Figure 8 0 0.5 1 2 3 Miles Infiltration Suitability wreoa hNAv Lava Nothing to Chmce I SVA M Location Map